Galactic Alliance history & background
History of the New Republic: The New Republic had survived the Thrawn threat to be faced with a new one, Grand Admiral Nagel became the Imperial Leader after Thrawn's untimely death. Nagel started his war against the New Republic with what seemed to be an endless supply of resources, a gigantic fleet, and an unending supply of stormtroopers. This matters to the galactic alliance because Nagel immediately declared war on the fledgling New Republic, and sent a multitude of assassins to thin the officer's ranks, causing planets to secede.
As many high-ranking officers were killed in the war, one shone above the rest. Commander Keller was promoted to Admiral and put in charge of all Naval Operations after a string of victories. Keller soon became a figurehead for the New Republic, even though many thought he didn't deserve the right to his rank. Life continued on in the New Republic, and the ranks of the military started to gain number once more. Later Nagel began to become more bold in his attacks, and finally attacked Corellia itself. The system was annihilated as Nagel's Fleets commenced bombardment of the planets, leaving only ruins behind. The New Republic knew the battle for Coruscant would be coming soon.
Admiral Keller immediately started stockpiling resources for both the battle and the aftermath. He had no doubt they would lose the battle and he wasn't going to leave the remnants of the New Republic defenseless. Then 'The Battle of Coruscant' came to the Galactic Republic's capital. The New Republic forces fought hard but had no chance in the beginning, the odds were so unevenly stacked against them that even certain corellian smugglers wouldn't ignore them. The New Republic retreated and the Imperial forces established the New Empire under Nagel's rule. It was a dark day.
With the recent destruction of the New Republic, after the Battle of Coruscant. The remaining planets and forces that fell under the New Republic banner have formed a Galactic Alliance, a rebellion against Imperial oppression. However, it is growing evident day-by-day that this Alliance is crumbling and destroying itself from the inside out.