The first island attacked by the Allies in a move to draw closer to Japan was:
Guadalcanal
Located in the Solomon Islands, Guadalcanal hosted a Japanese troop that was attacked by U.S. soldiers. This surprise attack started a series of clashes through the aid of continuous reinforcements from both sides. Nevertheless, the U.S. reinforcements eventually surpassed those of the Japanese.
In February 1943, the Japanese were outnumbered and had to evacuate their remaining men.