The Final League Pact War (also known as simply the Final War) was a military conflict fought between the Great Interstellar League and the Pact from 633 to 656.

The two super-states committed themselves to a state of total war after decades of tension following the League invasion of Pact space at the beginning of 633. The stagnation of the League economy, recent advancements in Pact weapons technology, and an increase in Pact support for insurgent groups within the League led to the fear that the Pact would initiate a first strike in the near future. To thwart this, the League launched its own invasion, Operation Pulse, and initially made great gains in simultaneous attacks across many systems. By 639, a fourth of Pact territory was under League control and only Admiral Wujuda's Seven Systems Campaign gave the Pact any significant victory. The Pact made the controversial decision to abandon many systems in order to solidify their defensive lines, and carried out scorched earth tactics to deny resources to the advancing League military. During the Battle of Meghedon the Pact destroyed their own FTL gate in the system, wiping out the League fleet and triggering the Blight, the period between 640 and 644 during which both sides freely used weapons of mass destruction. During the 644-647 cease-fire, the two sides agreed to the Typhon Accord, barring the further use of these weapons.

The resumption of the war in 647 with Operation Lavender saw renewed offensive operations by the League, none of which made a decisive breakthrough. An extended line of communication, Pact insurgency on conquered worlds, and unrest at home further hampered the League war effort. The Pact counteroffensive in 648 resulted in the liberation of many systems and a harsh blow to the League's military leadership when the Nomad Arsenic was destroyed during the Battle for the Gates of Hell. In 650 the Pact launched Operation Fall of the Moon, a coordinated set of raids into League territory intended to destroy the League's war making capabilities and morale. The damage to the League's infrastructure forced them to dispatch much of their front line space forces supporting the remaining occupied worlds to chase after the Pact invaders with limited success.

Word spread in late 651 that both sides had rebuffed an offer from the Amalah Empire to mediate a peace between them. Angry that peace had been thwarted and anxious to get back home to salvage what was left after the Pact raids, mutinies sprang up within the League military, demanding to be sent back home. Many League worlds rebelled against the League when they learned of the mutiny, conducting separate peace treaties and alliances with the Pact. Though the League was able to negotiate new terms for the remaining loyal systems to keep their allegiance, the internal disorder severally hampered their war making capabilities. A brief resurgence in League military victories at the Battles of Halfway and Nanotree were offset by defeats in the Anduduwa, Essao, and Penn Systems.

In 656, the Pact and its former League allies drew the League space force into one final battle in the Mbare Musika System. Both sides are nearly destroyed but the Pact emerged victorious. With the Nomads' Great Ones in the nearby systems now threatened, the League agreed to a cease-fire. Peace was negotiated by the middle of the year.

With much of the superstate in shambles or revolting, nothing stops the majority of the League systems from rebelling as well. By the end of 656, the League was reduced to 12 star systems and 95 billion citizens; roughly 20% of its former territory, and 13% of its pre-war population.

Peace and victory reveal the severe strains on the Pact social fabric, as many were disillusioned by the Pact's conduct of the war and the staggering cost of lives. Within the a year, many of the Pact's members withdraw from the alliance, leaving only 8 star systems and 79 billion citizens within its group of loyalists.

Fiore Campaign

Battle of Kirishima

Battle of Varuna

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