The First Exodus marked the height of the Terran Alliance. During this era, the first off-system colonies were established.
After almost a century, the hyperspace theories of Thomas Kearny and Takayoshi Fuchida had been proven correct. The Terran Parliament approved funding for the Deimos Project, the development of the first faster-than-light space ship.
The Race to Space
After the maiden flight of the TAS Pathfinder and its arrival in the Tau Ceti system on December 5, 2108, the Terran Alliance began a crash program to produce faster-than-light colony ships. The first such ship was the TAS Ark, which in 2116 established its first extrasolar colony on Tau Ceti IV. By 2123, corporate production of JumpShips had become feasible, and the race to space became the new, global Manifest Destiny.
During this first colonization wave, new planets were settled monthly. Eventually, disaster struck in April 2128, when the privately constructed and operated colony ship Liberator disappeared without trace. The Alliance Parliament quickly passed regulations, forcing colony ships to be escorted by Terran Space Navy ships, and installing planetary administrators as colonial governors.
The Separatist Conflicts
The Terran Alliance of the early 22nd century was still only an alliance dominated by the wealthiest states, not even uniting the entire planet. The sleeping conflict between the Separatist nations and the Terran Alliance not only fueled colonization efforts, but also created an atmosphere of constant threat.
After 2177, the Ryan Cartel's newly developed ice shipping process became the main source of drinking water for colonies, further increasing the pace of colonization. Rudolph Ryan himself was - after his death - revealed as a strong supporter of the colonies' independence and had often "lost" technicians or JumpShips full of colonization equipment in support of budding Separatist colonies, which his corporate subsidiaries had helped create in the first place.
Despite Ryan's support, not all Separatists and anti-Alliance groups emigrated off-world, but radicalized in the face of increasing Alliance oppression. Terrorist organizations like Elias Liao's New World Disciples sprang up. Quickly gaining notoriety, Liao's group was responsible for the death of no less than 26 heads of states, and 14 Terran Alliance Parliament members (and at least 135 bureaucrats, scientists, and technicians), further destabilizing Terra's political system. Rudolph Ryan himself was killed by an anarchist assassin in 2185.
The simmering conflict between the Alliance and the Separatists and the constant threat of nuclear terrorism finally erupted into a series of unification wars. By the early 23rd century, Terra was finally unified under the Terran Alliance. The Alliance itself, now without external opposition, began the slow process of unifying from an alliance of independent states into an actual federal state, although more through inertia than by design. 
During this period of consolidation, the Alliance Parliament (stuck somewhere between a discussion chamber and an actual legislative body) polarized into two opposite political parties - the authoritarian Expansionists and the slowly radicalizing Liberals. The Expansionists had informally been in power since the development of the Hyperdrive, while the Liberals had begun imitating the tactics of their successful opponents. 
Collapse and Isolation
The final Grand Survey, conducted in 2235, listed 628 colonized worlds in a radius of 250 light years. In May of the same year, Denebola declared independence, and just a year later, the Outer Reaches Rebellion began on Freedom.
While local protection treaties, such as the Chesterton Trade League had already been established for decades, the Alliance-appointed colonial governor's demand for extensive regulative rights was - in the face of the Alliance's overall benign neglect - the driving force behind an independence movement that rose to power in several loosely aligned colonies. When Terran troops first fought the well-entrenched insurrectionists, they were soundly defeated, to the shock of the Expansionists on Terra. 
The conflict continued well into 2237, with more and more declarations of independence reaching the Terran Alliance Parliament. Saddled with passive resistance and refusal of support from other colonies, the Terran forces finally realized the futility of their situation and returned home. 
Following this first defeat and with others soon following, the political situation on Terra turned into chaos, allowing the Liberal Party to oust the Expansionists in 2240. Unfortunately, the Liberals had become as radicalized as the Expansionists, and acted accordingly. For a while, even mentioning Terran offworld colonies was treated as a criminal act. Finally, the Liberals passed the Demarcation Declaration: from 2242 onward, all Terran colonies (aside from a 30 light years bubble around Terra itself) were released into independence, whether they desired it or not. The age of the First Exodus was over.
- Star League sourcebook, p.8
- Dropships and Jumpships, pp. 11-13
- Jihad Hot Spots: Terra, pp. 144-145
- Dropships and Jumpships, p.14
- The Periphery (sourcebook), p. 12
- House Liao: The Capellan Confederation, p. 8
- Star League sourcebook, p. 10
- Handbook: House Davion, p.19
- House Liao: The Capellan Confederation, pp. 9-10