Kerensky's dramatic exodus removed the last real obstacle to civil war. In December 2786, Minoru Kurita declared himself First Lord of the Star League, and the other four Council Lords quickly followed suit. Within months, war had engulfed the entire Inner Sphere.

The First Succession War lasted from 2787 to 2821, a conflagration of unparalleled brutality. The warring Lords of the five Great Houses cast aside the Ares Conventions, smashing cities, destroying vital industrial facilities, and butchering hundreds of millions of civilians. Few worlds escaped unscathed, and all were affected by the complete disruption of trade, commerce, and communications. By 2815, the warring states had lost most of their FTL shipbuilding capacity. The intense concentration of economic resources into military production had also forced a major drop in consumer goods production, creating a severe decline in trade. This loss of trade proved particularly disastrous for those worlds relying on high-tech water purification equipment. Without proper maintenance or spare parts, many of these facilities began to fail, forcing abandonment of the worlds or a return to iceship technologies. By the war's end in 2821, water-rich planets had become as strategically valuable as they had been 400 years before.

The peace of 2821 was uneasy, resulting more from exhaustion than any true reconciliation. Though no House Lord could claim to have made much progress toward his goal of dominion, too many atrocities had occurred to allow any sort of lasting settlement. From 2821 through 2827, the five surviving ruling Houses rebuilt as much of their military might as possible, concentrating their surviving scientists and engineers on those few worlds whose industrial capacity remained intact. Between 2828 and 2830, tensions along the borders of each rival state erupted, leading once more to all-out war.

The Second Succession War lasted from approximately 2830 to 2864, and was just as deadly, destructive, and indecisive as its predecessor. Hundreds of millions more died in countless battles across the Inner Sphere, though only a few dozen worlds ultimately changed hands. As the war destroyed more industrial facilities and killed off more scientists and engineers, some types of specialized knowledge and technology began to disappear entirely. By the end of the Second Succession War, what had become known as the Successor States' overall level of technological knowledge sunk to a level barely above that of Terra in the early 21st century. It was no longer easy to build advanced computers, large fusion power plants, or starships. Instead, the leaders of the Successor Houses began to cannibalize existing equipment for the spare parts necessary to keep their current war machines in working order.

After a second brief respite, the Third Succession War erupted in 2866. It began when advance forces of the Draconis Combine invaded the coreward portion of the Lyran Commonwealth; war soon spread across the Inner Sphere. In the years that followed, combat became such a fact of everyday life that the period become known simply as "the Succession Wars." Nonetheless, campaigns during this period never matched the violence of previous two wars.

At first, the decrease in destruction and bloodshed appeared to be more a function of each army's reduced resources than philosophical change in tactics. As time passed, however, and the exigencies of a scavenger economy took hold, each of the Houses realized it could ill afford further losses of vital resources. Gradually, an informal set of rules of war evolved, similar to the Ares Conventions. 'Mech units and armies still fought over possession of operational factories, but neither side attempted to harm the facility itself. (The losers simply consoled themselves with the idea that they would win the planet in the next war). Major 'Mech battles, especially between mercenary units, were often fought in stages, with both sides allowing enemy Techs to enter the battlefield during periods of truce to attend to damaged 'Mechs. Other 'Mech units, again especially mercenaries, revived the old tradition of surrendering to a superior force and paying a ransom to obtain their off-world release. Most important, everyone recognized the sanctity of any side's JumpShips, and strictly obeyed the prohibition against attacking such craft. After all, without JumpShips, the war for supremacy could not be waged at all.

A second outgrowth of the destructiveness of the Succession Wars was the rise of feudalism throughout the Inner Sphere. The central governments of the ruling Houses no longer possessed either the administrative machinery or absolute military resources to maintain centralized control over their territories. Instead, each House Lord ruled a hierarchy of planetary nobles. These nobles were often drawn from the leadership of his most elite 'Mech units, having won full authority over worlds in exchange for the pledged service of their BattleMechs.

Indeed, the years of conflict wreaked havoc beyond the borders of the Successor States, creating the phenomenon known as the Bandit Kings of the Periphery. As the wars raged back and forth along the frontier, dozens of 'Mech units - most often composed either the fragments of defeated units or mutinous mercenaries - fled into the vastness of the Periphery. Several of the units emerged again, often after a number of years, as "kings" of one or more small worlds seized by force of arms. By the end of the 30th century, more than 60 known small kingdoms and principalities ringed the Inner Sphere, creating the ever-present threat of raids and piracy to the frontier worlds of each Successor State.

This era of tentative stability lasted for roughly a century. Interestingly, it was a call for lasting peace that marked the end of a relative balance of power among the Great Houses and began the ferocity of the Fourth Succession War.

Recognizing humanity's slow but steady slide away from the glories of the Star League era and toward barbarism, Archon Katrina Steiner of the Lyran Commonwealth issued a Peace Proposal to the other House leaders in 3020. Only Hanse Davion, Prince of the Federated Suns, welcomed the initiative. Announcing that he would "take history by the throat," Davion began negotiations with the Archon. The result of these talks was the Federated-Commonwealth Alliance Document, which Prince Hanse Davion and Archon Katrina Steiner signed on Terra in 3022. In addition to trade and military agreements, the F-C Document contained a secret provision betrothing the Archon's daughter in marriage to Hanse Davion. Though the marriage would not occur until the twelve-year-old Melissa came of age, this was the first step on the road to eventual unification of the Lyran Commonwealth and the Federated Suns.

The other three Successor Lords were aghast at this sudden shift of power, which would lead to the eventual creation of a single state nearly as large as their three Houses combined. In October 3022, the Draconis Combine, the Free Worlds League, and the Capellan Confederation hastily signed the Concord of Kapteyn. The scope of the Concord was not as far-reaching as the F-C Document, however. It called mainly for an end to active hostilities between the three states, who now pledged mutual defense instead. This new relationship would also permit the three parties to coordinate their overt and covert efforts at derailing the Davion-Steiner alliance.

Perhaps most active in the covert attempts was the Capellan Confederation under the leadership of Chancellor Maximilian Liao. Liao agents had already subverted Hanse Davion's brother-in-law Michael Hasek-Davion, who was now providing them with valuable military intelligence. When the Chancellor next initiated a scheme to kidnap and kill Hanse Davion in order to replace him with a clone his scientists had created, he went too far. Davion eventually escaped capture and imprisonment and returned to his place on the throne. But he vowed revenge.

On 20 August 3028, Prince Hanse Davion and Archon-Designate Melissa Steiner were married at the ComStar headquarters on Terra. In attendance were all the important Steiner, Davion, Kurita, Marik, and Liao personages, as well as the great military commanders and other important persons of the Inner Sphere. Hanse and Melissa exchanged vows, and the Federated Commonwealth became a reality. At the wedding reception, the bride toasted the groom and bestowed him with gifts. When it was the groom's turn, he rose with a smile. In honor of their marriage, he said that he had for Melissa a vast prize. "Here, my love," the Prince of the Federated Suns said triumphantly, "I give you the Capellan Confederation."

And so began Operation Rat, a surprise attack on nine Capellan worlds that was occurring that very day. But this was only the beginning of a much larger offensive against the Capellans and against the Draconis Combine - the start of the Fourth Succession War.

The main weight of the attack fell on the Capellan Confederation. Having discovered Michael Hasek-Davion's treachery, Hanse Davion had been using him as a conduit to feed faulty intelligence to Maximillian Liao. Justin Allard, a Davion agent, in a position of power and authority in House Liao's military intelligence. The Capellan Confederation did not have a chance, and lost half its worlds.

The Draconis Combine fared a bit better, losing 53 star systems to the invading Lyran Commonwealth forces, but gaining 15 from attacks against the Federated Suns. Indeed, Theodore Kurita, heir to the Combine throne, was preparing to launch his own strong counteroffensive just as the war suddenly ground to a halt. Having achieved most of their objectives in the Capellan Theater of Operations, Hanse Davion and Katrina Steiner declared victory and a cease-fire in 3030. Each had his or her reason for wanting an end to the hostilities. The economy of the Federated Suns was reeling under an interdiction on interstellar communications that ComStar had imposed. As for Katrina, her realm was threatened by the growing power of separatists who opposed the Federated Commonwealth alliance.

Though the two-year-long Fourth Succession War was relatively short, it was a bloody conflict. Despite the constant border fighting that characterized the Third Succession War, the great states of the Inner Sphere had by then recovered somewhat from the ravages of the first two Succession Wars, and the political and social landscape had not much changed. In contrast, it would be 20 years before all the social, political, and military effects of the Fourth Succession War could sort themselves out.

In 3029, ComStar came under the leadership of Primus Myndo Waterly. The communications interdiction, which had been imposed on the Federated Suns after an alleged Davion attack on the ComStar station at Sarna, was lifted after Hanse Davion granted ComStar the right to garrison all its Federated Suns stations with its own troops. Similar arrangements with the other governments of the Inner Sphere soon followed. By the year 3050, ComStar had more than 50 BattleMech regiments under its control.

The boundaries of the Inner Sphere began to shift as a result of the war. In the Free Worlds League, the Duchy of Andurien seceded and allied itself with the Magistracy of Canopus. Ten years would pass and both Captain-General Janos Marik and his son Duggan Marik would die before Thomas Marik, the new leader of the Free Worlds League, would recover the Duchy.

Maximilian Liao went mad during the closing days of the war, eventually committing suicide in 3036. With over half of Liao's planets under the control of the newly formed Federated Commonwealth, the mantle of the Capellan Chancellorship fell on the shoulders of Maximilian's youngest daughter, Romano Liao. Despite losing more worlds when the St. Ives Compact seceded from the Confederation, Romano used sheer ruthlessness and brutality to fight off an invasion by the Duchy of Andurien and to rebuild the Liao military. Though the Capellan military did not approach its pre-Fourth War numbers, it became feared for the utter fanaticism of its troops.

Secession fever also reached into the Federated Commonwealth and the Draconis Combine. As Deputy for Military Affairs, Theodore Kurita skillfully maneuvered to turn the Combine's rebellious Rasalhague District into a bargaining chip with ComStar. In exchange for Rasalhague's independence and the right to garrison its hyperpulse stations with its own troops, ComStar agreed to supply the Kuritans with enough BattleMechs to rebuild their army. The Lyran Commonwealth, which had used Rasalhague rebels extensively during the four Succession Wars, had by now occupied more than half the district. Faced with the Combine's support for Rasalhague independence, the Lyrans were forced to give up these worlds. With the stroke of a pen, Theodore Kurita created a neutral buffer state that reduced his borders with the armed might of the Federated Suns by more than 30 percent. Not all Kurita troops supported the move, however. A rebellion known as the Ronin Wars erupted inside the Free Rasalhague Republic, but it was quickly put down by loyal elements of the Draconis Combine Mustered Soldiery and the Republic's newly formed KungsArme.

Theodore Kurita's wisdom in granting Rasalhague its freedom became clear in 3039. In that year, the Federated Commonwealth launched another major war, this one aimed at eliminating the Combine once and for all. Having rebuilt his army with ComStar-supplied BattleMechs, Kurita was able to concentrate his troops against the invaders, stopping the F-C forces' attack dead in their tracks.

By 3040, the Inner Sphere had settled down to its normal state of continual, low-intensity skirmishing, with no side making any major gains or taking any major losses. Nevertheless, the sheer size of the Federated Commonwealth made it seem only a matter of time before it would dominate the Inner Sphere, uniting the many worlds once more under one rule.