The Battle of Liberty Island is a conflict which occurs in 2072 and is the culmination of the invisible war. The Battle takes place on Liberty Island, New York City, around the former Statue of Liberty and the former UNATCO HQ.
The battle is fought between the forces of ApostleCorp (led by JC Denton and Paul Denton), the Illuminati (led by Chad Dumier and Nicolette DuClare) and the Knights Templar (led by Saman). In the end, however, the outcome of the battle is decided by Alex Denton, who gains access to the Aquinas Hub located inside the UNATCO HQ ruins.
The battle has four possible outcomes. Alex could upload the Aquinas Hub to one of the three warring factions, or he/she could destroy all three factions, heralding a new era of war and natural selection from which the Omar would eventually emerge victorious.
The events of the Battle make up the climax of Deus Ex: Invisible War. It should be noted that the term "Battle of Liberty Island" is never used in-game and is an invention.