Inner Sphere

In the fictional BattleTech universe, the Inner Sphere is the region of interstellar space surrounding Earth to a radius of roughly 500 light years. The five Successor States, each ruled by an ancient Great House, are the Inner Sphere's dominant power in the setting's "modern" era, although other nations, empires, and independent worlds have ruled parts of the Inner Sphere in the past, and continue to exist. After the fall of the Star League, the Inner Sphere fractured as each of the Great Houses attempted to secure rulership during the Succession Wars.

Politics and Society
The five Successor States are the most enduring political entities in the Inner Sphere. From c. C.E. 2300 to 2787, the Inner Sphere was divided into five "pie wedges" around a central, roughly circular core: the five Great Houses and the central Terran Hegemony. When the Star League collapsed in 2787, the Great Houses divided the Terran Hegemony piecemeal among themselves, and since that time have waged a series of wars for supremacy, known as the Succession Wars.

The political structure of the Successor States is essentially feudal, with the exception of the Free Worlds League, which has a federal structure, at least at the highest levels of government. Planetary governments in the Inner Sphere span the entire range of political structures, from democracy to dictatorships, although authoritarian forms of government are considerably more common.

At various times, other political entities such as the Free Rasalhague Republic or the independent worlds and small states of the Chaos March have shared power with the Great Houses, often acting as buffer zones between their more powerful neighbors.

The Periphery surrounding the Inner Sphere is home to a few nations of moderate power and independent worlds cut off from civilization by the collapse of the Star League. The Inner Sphere perceives the Periphery as a backwater. The Periphery is also a safe harbor for pirates, criminals, and refugees from the Succession Wars.

History of the Inner Sphere
See also History of the BattleTech universe

Early History
The history of the Inner Sphere began on December 5, 2108, when the TAS Pathfinder successfully completed the first FTL round-trip voyage between Terra and the Tau Ceti system. In 2116 the first permanent colony was established on Tau Ceti IV, also known as new Earth. In 2172 the First Grand survey reported that there were more than 100 Human-colonized worlds. In 2234, the number of colonies had expanded to 600.

The earliest colonies were small and dependant on technical support and supplies, particularly of water, from Terra. However, in  2177 the Ryan Cartel began to operate a fleet of iceships, jumpships designed to carry frozen icebergs from water-rich systems to water-poor ones.

As the colonies became materially self-sufficient some of the colonies began to chafe under the authority of the distant Terran Alliance government. The first world to openly declare independence from Terra, Denebola, a colony on the outer rim of human occupied space, did so in 2236. As additional worlds began to follow Denebola's lead, the Terran government sent a force of Colonial Marines to Denebola to make an example of the upstart colonists, but severely underestimated the size and sophistication of the Denoboluan army. Consequently, the small force of Colonial Marines the Terran Alliance sent to Denebola was decisively defeated.

After the defeat of the Colonial Marines on Denebola other colonies began to declare their independence from Terra. Within the Terran Alliance, the defeat of the Colonial Marines caused a power shift within the government. The Expansionists were pushed out of power, and the Liberals gained control of the government. The Liberals immediately began to grant independence to the colonial worlds, whether they wanted it or not.

By 2242, the extent of Terran holdings was no further than 30 light years from Terra, no more than a single jump for a jumpship. It was during this period that humanity first colonized worlds at the farthest reaches of what is known today as the Inner Sphere. Economic depression and political strife caused many of Terra's brightest minds to emigrate to the newly independent colonies during the latter half of the 23rd century, a period which became known as "the Exodus." During this period, humans colonized over 1500 new worlds in a sphere around Terra almost 300 light years across.

Among the outer colonies innumerable small kingdoms and confederations began to form, and slowly larger, more stable states began to emerge from the morass. In 2271 the governments of three small worlds in the outer colonies signed the Treaty of Marik and formed the Free Worlds League, the earliest of the six great star empires which would eventually dominate the Inner Sphere.

Rise of the Great Houses and the Age of War
In September 2314, the Terran Alliance collapsed amid fighting between the Liberal and Expansionist factions. Moving to avert a general crisis, Fleet Admiral James McKenna intervened between the two sides with loyal Alliance military forces. With the civilian government in shambles and the military behind him, Admiral McKenna dissolved the Terran Alliance and named himself Director-General of a new political entity, the Terran Hegemony. Director-General McKenna was determined to reassert Terra's dominance over the colonies, and used Terra's political, economic, and military might to establish the Terran Hegemony's control over about 100 worlds by the time of his death in 2339. In 2340, Michael Cameron, James McKenna's nephew, took over the office of Director-General, beginning the Cameron dynasty.

By 2389, the six major powers in the Inner Sphere had all been established, and the pattern of dynastic rule which characterizes the Inner Sphere was established. Soon afterwards, these states began to contest with one another for supremacy. In 2398 the Capellan Confederation and the Free Worlds League went to war over the Andurien system. The next century and a half came to be known as the Age of War as the states of the Inner Sphere clashed in a series of border conflicts as their expanding borders began to bump up against each other.

In 2412, after fighting in the Tintavel system resulted thousands of civilian deaths, the representatives of six Inner Sphere and two Periphery governments signed the Ares Conventions, which sought to promote limited warfare by prohibiting attacks on civilian population centers. While the Ares Conventions were successful in limiting warfare, they had the perverse effect of lowering the threshold of provocation needed to start a war by lowering the cost of war. Thus, war became a continuous fact of life in the 25th century.