Dominion War

The Dominion War was a two year interstellar conflict between the allied powers of the Alpha Quadrant and forces from the Gamma Quadrant (along with some Alpha/Beta Quadrant allies of their own.) Prior to a full blown war, the Federation and Dominion had enjoyed a quiet enjoyment with sporadic border skirmishes, however matters escalated when the USS Odyssey was destroyed with over 1,000 souls lost. Through the efforts of the crew of Deep Space Nine, it was established that the Dominion was ruled by the Founders, seen somewhat as overlords by its allied factions (the Vorta, Jem'Hadar and the Breen.) Able to shapeshift, the Founders infiltrated the governments of the Federation, Klingon Empire, Cardassian Union and Romulan Star Empire and caused all manner of unrest.

The balance of power in the Alpha Quadrant took a turn for the worst when the Cardassians signed a military alliance with the Dominion, and the Romulans signed non-aggression pact, however evidence of a Dominion coup soon encouraged them to ally with the Federation and the Klingons.

At the height of the war, forces from both alliances fought with heavy losses, making it the most significant and devastating war in galactic history. Not every member state of the Dominion was as loyal to its leader however; the Cardassian Union's military general soon became weary of the conflict and sickened at the Founders view of their troops as cannon fodder. Legate Damar, the Cardassian military leader, staged a rebellion on Cardassia which quickly took hold in the public conscious. The Founder became enraged at the prospect of being betrayed, and ordered the aerial bombardment of Lakarian City, killing millions of civilians. News of the slaughter reached the Cardassian ships during the height of a massive conflict, with all Cardassian forces switching sides and turning their guns on the Dominion. The Cardassian Union's hasty new alliance with the Federation was critical in winning the war.

At war's end, the effects of it would last long into the 25th century. The Cardassian Union was no longer a military force in the galaxy, the Federation and Klingon Empire were set back by a decade and the Romulans suffered massive divisions in loyalty, until the Hobus Supernova made matters even worse. The after effects of the war are discussed below:

The 4800 Incident
In 2412, almost 5,000 Dominion starships thought lost in the Bajoran Wormhole during the conflict were ejected into the path of Deep Space Nine during a critical Federation conference. The ships had been thrown forward in time by the wormhole aliens and, assuming the war was still in effect, assaulted DS9 and took control of it. The station was later taken back however by the crew of the USS Hunt.

The Cardassian True Way
The demilitarisation of Cardassia was not welcomed by all, with splinters of the military forming a group that called themselves The True Way. Led by Gul Madred, the True Way presented somewhat of a minor threat to the Federation until it became apparent they were planning terrorist attacks amongst its interests.

The Romulan Civil War
Massive upheaval in the Romulan Star Empire was exacerbated further after the war, both with the Shinzon Incident and the Hobus Supernova.