Doing consistent lore analysis for Star Trek can be challenging at the best of times. Some of this is just due to the sheer scope of the expanded universe and the difficulty of accessing some sources. Another challenge is legal - Trek licensing is a tangled web that spans years, often between rival companies and under terms that don't completely house the data rights with Paramount/CBS. This gets especially tricky with things like sourcebooks and role-playing games, which by necessity tend to be packed with lore and background information, but often can't reference each other. For example, you won't see the Modiphus Star Trek RPG's Klingon Adventures referencing the FASA Star Trek RPG's Klingon Intelligence Manual, because even though they're both licensed Star Trek products, the FASA material isn't clearly usable by Modiphus from a legal perspective. Likewise, Star Trek Online can't feature the visual designs from the excellent Klingon Academy game because Interplay retained rights to much of the derivative material they generated for their family of Star Trek games. 

So when we look at Star Trek lore as fans, we have to synthesize multiple, sometimes conflicting sources (either because the sources themselves are dated, or because they're reinventing the wheel to fill in holes that they can't legally just carry forward previous lore). In this case, we're primarily looking at the following sources for our history:

• The Klingons: Game Operation Manual by FASA (FASA Star Trek RPG)
• Prime Directive Klingons by Amarillo Design Bureau (Star Fleet Battles)
• Klingon Adventures by Modiphus Entertainment (Star Trek Adventures)

We'll also be leaning on Memory Alpha for aggregated information about Canon, Memory Beta for aggregated information about licensed fiction, and the Star Trek Online wiki for information about STO's episodes. Finally, at times we may reference the works of Guenther & Sofia, such as the Federation Reference Series and other FASA works such as their various movie sourcebooks and the Next Generation Officer's Manual. 

By the time of Captain Kirk's first five-year mission (the late 2260s), scientists in the Federation and elsewhere had started to suspect that the ancient race known as the Preservers had played some role in the substantial similarities between the countless humanoid life forms populating the galaxy. There was evidence that the Preservers had in several cases transplanted "seed" populations from underdeveloped planets to different star systems in an effort to preserve those peoples' unique biological and cultural characteristics. One hypothesis posited that the Preservers had in fact seeded all humanoid life throughout the galaxy approximately two billion years ago, with their subsequent transplantation efforts reflecting only the very last stages of their aeon-spanning project.

This theory was wrong, but only in its interpretation of the facts. In 2369, famed archaeologist and explorer Captain Jean-Luc Picard discovered compelling evidence that an even earlier race than the Preservers - the so-called Progenitors - had indeed seeded suitable planets throughout the galaxy such that they would eventually develop humanoid life. The Klingons, who had always rejected the Preserver Hypothesis, were forced to grudgingly accept the reality of the Progenitor seeding program when confronted with the evidence. Beyond this "first step," however, biologically and behaviorally modern Klingons evolved through natural processes in the environment of their home world, Qo'noS. Located in the Klinzhai star system, Qo'noS would be classified as only marginally habitable by many other humanoid species, with its 1.23G gravity field and violent climate system. 

Biologically modern Klingons emerged in the archaeological record approximately 500,000 years ago, but the emergence of behaviorally modern Klingon civilization is difficult to trace. 

Though not fully comprehended by the Klingons of the time, Qo'noS was far from unfamiliar with alien invasion. In ancient times, the Furies dominated prehistoric Klingons; subsequently, an unknown species established themselves as deities on the homeworld. It's unclear how or why the Furies departed Qo'noS, but Klingon legend speaks to the departure of the other species: growing tired of their rule, the Klingons rose up and destroyed their would-be gods. What followed was an age of war.

Starting around 9000 BC, Qo'noS existed in a state of perpetual war first between city states and later between fledgling nation-states. By about 7500 BC, the modern concept of honor within Klingon society had started to emerge, strongly influenced by this period of warring states. This roughly correlates with the beginning of the cultural split between sea-dwelling and land-dwelling Klingons, attested circa 7000 BC in an epic poem about the war between komerex Nevre ("the Northern Empire*") and falgav a'kavna ("the Crescent Islands"). *While komerex is traditionally translated by historians as "Empire," a more accurate translation is "Imperial state," in the sense of the throne-state ruling over vassal kings. wo' (which is also commonly translated as "Empire" and is the word used in the native phrase for 'Klingon Empire') refers to a unitary, centralized state with an Emperor at its head.

This state of affairs continued until approximately 1000 BC, when an asteroid impact caused massive ecological damage and fundamentally broke the balance of power amongst the warring states. The next two thousand years were marked by increasingly brutal competition for scarce resources that saw many weaker states destroyed or absorbed into their neighbors. This pattern of competition and consolidation finally reached its peak in 854 with the ascension of Kahless the Unforgettable to rule over all of Qo'noS.

Despite the long years of stagnation prior to the coming of the asteroid, the final two millennia before Khaless the Unforgettable united the Klingon Empire (tlhIngan wo') had seen significant scientific progress. Of course, this was in large part driven by necessity and tended to focus on areas of military interest as well as improvement in agriculture and food storage. Nevertheless, the Empire under Kahless and his heirs was well positioned to undergo rapid development. Only 70 years later, having long grasped a generally accurate model of spacetime and understanding the theoretical concepts behind creating a warp field, Klingon astronauts - who had already explored the moons of Praxis and Corvix in slower-than-light spacecraft - made the first experimental trip in a warp-powered craft. 

Unfortunately for the Empire, they had little time to enjoy this breakthrough. In 972, an insectoid race known as the Hur'q invaded Qo'noS and overwhelmed its armies. Despite ongoing resistance that was a futile as it was heroic, the Hur'q consolidated their position on the planet and, after destroyed the Klingons' nascent space forces, set about plundering the planet. The Hur'q not only stripped Qo'noS of resources, but confiscated many cultural treasures and shipped them off-world. The Hur'q occupation is a major reason why so little is known about early Klingon history outside of myth and legend.

While open resistance gradually faded, it did not end. The Hur'q never settled Qo'noS with sufficient numbers to dispense with the local population, and the Klingon Empire was allowed to maintain some modern infrastructure to allow them to efficiently serve their new masters in the denuding of their world. Over literally centuries, Klingon scientists painstakingly discovered their would-be masters' weaknesses and industrialists secretly produced and stockpiled arms. Despite the awful fates of countless Klingons whose efforts were discovered, the long plan of revenge finally bore fruit, with Emperor Kreddik leading a planetwide uprising that finally drove away the Hur'q. 

When the Hur'q finally departed Qono'S in the 1300s, almost all of the Empire's mineral wealth was gone and all of its spacecraft had long since been destroyed. Recognizing the fundamental instability of the post-Hur'q Empire, a faction led by General Ch'gran urged the Klingon people to reach for the stars. Citing the final words of Kahless the Unforgettable, he called on the Klingon people to venture into the black sky and seek out new worlds to conquer in the name of the Empire. Ch'gran was lost some time later while attempting to navigate the Betreka nebula with a fleet of captured Hur'q ships and hastily-built Klingon vessels, but his sacrifice was the final crystalizing event needed to awaken the Klingon people to the larger universe. 

Even as it became increasingly clear that the Empire was teetering on the edge of societal collapse from resource depletion, the Empire used what little strategic reserves it had left to build seven huge colonization ships, which they dispatched to nearby systems. The worlds these ships claimed for the Empire - notably Ty'Gokor and Boreth - would go on to be the core of the Klingon Empire in years to come. Of course, this expansion did not come without conflict, including fierce battles with the Samnatti people of Ty'Gokor, but in the end the Imperial forces, now under the reign of Emperor Kaldon. 

However, this spurt of expansion came at a severe price, and Emperor Kaldon also came to preside over the collapse of the First Empire. Even the late discovery of rich mineral deposits on the moon Praxis was not enough to reverse the disintegration of civilization, and a long dark age followed. Qo'noS was the first to fall, but all of these early Klingon colonies experienced a certain level of backsliding, with none of them retaining warp propulsion of FTL communication. 

600 years after the time of Kahless the Unforgettable, the sea people of Qo'noS reinvented the steam engine and revolutionized ocean-going trade in the 1500s. The restoration of maritime trade routes helped shake Qo'noS out of the late pre-industrial statis that it had settled into after the collapse, and saw a slow mark start towards recovering what they had lost in the aftermath of the Hur'q occupation. In 1634, the sea people united to form the komerex dexitlhIngan - the Empire of the True People - and lodge a claim as successors to the fallen Klingon Empire. The continental nations rejected this claim, leading to a new age of war. 

In 1924, the war took a decisive, and unexpected turn. Armed with newly rediscovered nuclear weapons, the KDT attacked the capitals of their main rivals, hoping to finally end the long conflict with a decisive blow. However, this attack had the opposite effect; outraged by indiscriminate destruction caused by the nuclear weapons, the continental states finally united and overwhelmed the KDT in only three years of combat. Both sides in the war had already started developing rudimentary space rockets, and with peace restored new efforts were launched to access the mineral wealth of the moon Praxis. In the years that followed, the people of Qo'noS also rediscovered ruins of the small colony on Klinshai's outer planet Kobek, which had not survived long after the fall of the First Empire. Seeking to reclaim what they had lost, Kobek was recolonized and became the first vassal world under Qo'noS control. 

Despite the end of the long war, Qo'noS was not united. The Klingon High Council, much like Earth's United Nations, was almost irreconcilably split along ideological lines. Every issue, from resolving local disputes, to distributing mining concessions on Praxis, to setting taxation and emigration policy for Kobek, became hopelessly bogged down in Council debate. Moreover, new fractures were forming within the allies who had defeated the KDT, and other than agreeing to completely ban nuclear weapons, key recovery programs quickly ground to a halt. Notably, the international warp drive program soon dissolved as each scientist returned to their home countries to pursue their research under new national efforts.

In 1967, Qo'noS received an unexpected visitor: a starship from Ty'Gokor. However, while the ship's commander was a Klingon, much of his bridge crew was not. The starship explained to Qo'noS, that the people of Ty'Gokor had made contact with an ancient and powerful civilization known as the Old Kings. In exchange for their vassalage, they had received the support and resources they needed to restore their civilization to pre-collapse levels and beyond. Now, as dutiful vassals, they were voyaging to the other Klingon colonies - and to the homeworld - to recruit them into the Old Kings' service.

The arrival led to great internal debate on the High Council. Ultimately, as with so many other matters, it settled into stalemate. But as individual nations began to pledge their service to the Old Kings and immediately receive generous technical aid, the holdouts' position became untenable. The High Council reluctantly formally pledged their vassalage to the Old Kings later that year, and found themselves expected to represent not only Qo'noS but also the other First Empire colonies. While the Council's effective "hands-off" approach delighted the distant colonies - long accustomed to autonomy - it only continued to escalate the frustration and dissent on Kobek and Praxis. 

In 1980, the High Council discovered that the leadership on Kobek had been hoarding illegal nuclear weapons and was planning on launching a rebellion to overthrow the High Council and seize control of the Klingon worlds. While a preemptive strike prevented the rebellion, the Kobek rebels detonated their own cache of arms before their defeat, rendering Kobek uninhabitable and deeply shocking the people of the homeworld. Over the next 40 years, as they watched Kobek slowly disintegrate from gravitational tidal forces, malaise over the paralysis of the High Council and their new lot as vassals slowly boiled over into anger and a demand for change.

An important footnote in this era occurred in 2016, when a Klingon-commanded Old Kings vessel encountered a Vulcan starship near Ha'toria. there is evidence that the Old King's Empire stretched as far towards the future Federation central worlds as Epsilon Eridani, was likely deep within their space. The Klingon commander refused communication and destroyed the Vulcan ship; this led to the policy of the so-called Vulcan Hello, where Vulcan ships would open fire on Klingon ships first, then offer communications. 

In 2022, a naval officer named Kahless, son of Riskadh, launched a coup that overthrew the High Council and placed Qo'noS under military rule. However, the Old Kings demanded a civil government to answer to them, and any plan of permanent military rule was reluctantly abandoned. Instead, Kahless declared himself Emperor and instituted a new Imperial High Council to serve as its civil government, but who were ultimately answerable only to him. The few nation-states that resisted were quickly quelled by the militry, and Kahless appointed Kagran, son of D'Kariv, to serve as his chancellor and regent when he could not personally oversee the High Council.

Kahless did not have long to savor his accomplishments. The Old Kings soon directed Kahless to return to their service and embark on a campaign of conquest. In 2026, Klingon-led Old Kings naval forces entered and subjugated the natives of Delta Khinian II, becoming vassals of the Old Kings and de facto servitors of the Klingons. This would set the stage for the first war between the Klingons and the Romulans, when a Romulan colonization fleet reached Delta Khinian and destroyed the small Klingon garrison before claiming the system for themselves. The Old Kings did not accept this intrusion into their territory, and ordered Kahless to lead his forces against the Romulans.

The war reached its peak in 2046 when Kahless, leading the Old Kings' fleet, died in a glorious battle that saw the Romulans entirely ejected from Old Kings space. From this point, Klingon history started to describe Kahless, son of Riskadh as "Kahless, Who Is Not Forgotten." A year later, Kagran formally succeeded Kahless as Emperor and presided over many years of on-again-off-again war with the Romulans. Regular skirmishes continued until 2069, and by the 2080s, the Klingon Empire has pushed the Romulans' borders back to the edge of what will come to be known as the Triangle Zone, though Klingon presence in the Taurus Reach and other adjoining areas remained very sparse outside of a few colonies and space stations.

In 2069, Emperor Koth died, sparking a succession crisis that nearly led to civil war. To head off that outcome, the High Council seized control of many of the Emperor's powers, reorganizing the government and formally declaring the Second Klingon Empire. Importantly, the Chancellor of the High Council would no longer serve concurrently as Imperial Regent, but would instead carry executive authority under the Chancellor's office. The Old Kings appeared to accept this change without comment, though under the reign of Chancellor Mow'ga the Kings set the Klingons against the Breen, far away in the Alpha Quadrant, with orders to conquer that species. The fleet sent there, which included many of the Empire's most experienced naval commanders, never returned.

In the years that followed, the pace of conquest under the Old Kings slowed and then entirely stopped. Communications with the Klingons' masters became increasingly sparse, until in 2140 the Old Kings ordered all ships to return to their home ports. On their arrival, the Kings ordered their crews to disembark, before ordering the same for all space stations and orbital production facilities. At the same time, large numbers of transports started to arrival at the various vassal worlds, carrying the population of colonies that were not yet self-sufficient. Finally, the Old Kings dismantled (forcibly when neccessary) all industries related to FTL drive production and communications, wiped navigational databases, and generally did whatever they could to revert their vassals to a pre-warp-travel state. 

With their work complete, large fleets of Old Kings ships departed from their vassal systems on courses that appeared to carry them towards the edge of the galaxy. The Old Kings were never seen again. Harkening back to ancient tales of the Hur'q departure, the Klingon Empire did not waste time in acting. Using chemically propelled rockets they still possessed the industrial base to produce, Klingon astronauts reached Qo'noS's orbitals and soon discovered that many Old Kings ships had been left behind. After stripping some ships for parts needed to restart key industries, the remaining ships became the nucleus of the Deep Space Fleet. Their first mission was to reestablish contact with the other major Klingon worlds, which they found had undertaken similar courses of action and acquired their own supply of abandoned spacecraft.

Under the guidance of Chancellor M'Rek, the Empire moved swiftly to secure its territory and to bring as many former Old Kings vassals under their control as possible. Likewise, even though the Empire was continuing to claim more abandoned Old Kings starships as late as 2159, the Deep Space Fleet almost immediately recognized that they could not sustain these old ships in the long run, and almost immediately started building new starships of native design. These ships were far less capable than the Old Kings types, but they were still more than adequate to secure the frontier against the Romulans and other contemporary threats. 

Now the masters of their own destiny, the Klingons had to contend with a hostile galaxy where they no longer could count on the protection of the Old Kings' vast empire. While many former vassals had eagerly accepted service under Klingon leadership, others had refused or had already joined with rival neighbors. In other cases, the Klingons had succeeded in persuading or conquering a prize, only to be forced to let it slip from their grasp because they lacked the resources to maintain their grip. In one particularly galling case, the former Old Kings vassals known as the Vergara staged a fleet-wide mutiny in an attempt to seize control of the Deep Space Fleet. While the mutiny was put down and the Vergarans severely punished, it highlighted the risks borne by the Klingons in their new role of masters dominating a multi-species empire.

By 2170, the Klingons had started large-scale construction of new starship classes that, while still not quite as powerful, had the capability of displacing the Old Kings ships. This first generation of "modern" Klingon warships, such as the BortaS class, also featured enhanced internal security features intended to thwart future attempts at mutiny by the crew. These new ships were put to the test in 2184 when the Klingon Empire encountered the Lyrans, a Kzintoid (bipedal, feline-like) species who they had only had occasional contact with during the reign of the Old Kings. Hostilies flared almost immediately, though much of the war was characterized as a race to control uncharted territory rather than directly invade either party's territories. The war (and land grab) continued until 2187, when the Lyrans drastically shifted forces to contend with a new threat they had encountered beyond the extent of Klingon-explored space.

Another war followed in 2193-2197 when the Klingons first encountered the Mirak Star League, a confederation of Kzintoid species who the Klingons would later discover were mortal enemies of the Lyrans. By the time the war ended, the Klingons learned that between the Lyrans and the Star League, their access to the distant reaches of the Old Kings' empire, where they had once fought the Breen, were cut off from them. Throughout all of this, they were also aware that the new alliance between the Vulcans, Andorians, Tellarites, and Earthlings was rapidly expanding and consolidating its territory, further boxing in the Empire.

The United Federation of Planets proved somewhat challenging to the Klingon Empire in policy terms. Until now, the Empire had tended to categorize foreign powers into three categories:

• Warrior races, to be challenged and competed with for resources and territory
• Inconsequential races, to be dominated - either by diplomacy or military force - and then ignored as long as they provided suitable tribute to the Empire
• "Children playing at war," to be militarily crushed with the utmost brutality, with the goal being that they either rise to become warrior races, or retreat into inconsequentiality

The Empire's first contact with the soft, diplomacy-oriented, friend-seeking Federation caused the to relegate them to the 'inconsequential' category, but later, as they learned the Federation had fought victorious wars against both the Kzinti and the Romulans, and recognizing their esteem for the Andorians as a fellow warrior race, thinking started to slide towards considering the Federation to be a worthy strategic competitor. 

The formal first contact between the Empire and the Federation (as opposed to the Federation's various precursor states) occurred in 2217. At the time, the Empire was involved in yet another territorial war with the Star League, the Lyrans, and the Hydrans (the aforementioned new enemy that had helped draw down the first Klingon-Lyran war), and perceived another conflict brewing in the future with the Holy Order of Kinshaya. Quickly dismissing the Federation as inconsequential, they dispatched ambassadors and intelligence operatives to study the best way to co-opt the Federation while allowing civilian trade to open between the two polities. In 2219, when the Federation found itself drawn into a conflict with the Mirak Star League, the Empire provided military advisors to help the Federation counter the League's tactics. 

After witnessing the outcome of the war with the Star League and receiving intelligence reports about the Earth-Romulan War and United Earth's multiple conflicts with the Kzinti Patriarchy, the Empire started to reassess its view of the Federation. While trade was not yet cut off, the Empire started planning contingencies to counter the Federation. This ultimately led to the Klingon-Federation War of 2234-2235, when the Klingons directly challenged the Federation's territorial declarations (which overlapped several systems that the Klingons also planned to take control of). The Federation fought the Empire to a standstill on the frontier, but then sought a diplomatic settlement. This caused a serious difference in understanding about the resolution of the war.

The Federation perceived that the war was essentially a face-saving measure for the warlike Klingons; that they needed to make a show of military strength before coming to the negotiating table in order to avoid the appearance of cowardice. The Klingons portrayed the Federation as unwilling to fully commit to the war, and interpreted the diplomatic settlement as demonstrating that the Federation was fundamentally unable to sustain a war effort for any length of time. This led to the Klingons to conclude that the Federation belonged to the fatal third category of 'children,' and set the stage for the brutal Four Years War of the late 2240s.