Federation-Borg War

"Your futile ressistance has been crushed. Your race and tehcnology will be assimilated. We Are The Borg" 
The voice of the Cube 670
The Federation-Borg War was a war between the United Federation of Planets and the Borg Collective from the year 2407 to 2450. The war ended in the Federation's dissolution and the near assimilation of the human race and of every race in the Alpha Quadrant by the Borg. The survivors of the war, except for the surviving Klingons, banded together to create the Alpha Resistance.
==Beginnings==
"Sometimes I wish the Federation was never born! It's tearing itself apart! The Golden Age is over! One more war and the Federation is gone!" 
The Andorian Chancellor's reasons for withdrawing from the Federation.
In 2377, the USS Voyager returned home to Earth after Admiral Kathryn Janeway helped them by seizing and later destroying a transwarp conduit built by the Borg, the Borg Queen was destroyed in the process with that, Starfleet thought the Collective was destroyed. THey were wrong.
The Borg Collective quickly assimilated a new queen and set out on a mission fo expansion. By the end of 2398, THe Borg assimilated every species, even the Kazon and Specie 8472, in the Delta Quadrant. This went ocmpletely unnoticed by Starfleet
In the Alpha Qudrant., Starfleet and the United Federation of Planets had only thirty eight starships left as a result of a short, but destructive war against Klingon rebels. Historians would call this The Calm Before the Storm. Because of the near-destruction of the Federation, planets started seceding from the Federation to fend for themselves. The Federation was soon reduced to a number of just 170 planets.