From May 1942, when the Battle of the Coral Sea was fought, until December 1943, the Solomons were almost constantly a scene of combat. Although U.S. forces landed on Guadalcanal virtually unopposed on August 7, 1942, they were soon engaged in a bloody fight for control of the islands' airstrip, which the U.S. forces named Henderson Field. One of the most furious sea battles ever fought took place off Savo Island, near Guadalcanal, also in August 1942. Before the Japanese completely withdrew from Guadalcanal in February 1943, over 7,000 Americans and 21,000 Japanese died. By December 1943, the Allies were in command of the entire Solomon chain.

The large-scale American presence toward the end of the war, which dwarfed anything seen before in the islands, triggered various millennial movements and left a lasting legacy of friendship. Following the end of World War II, the capital was moved from Tulagi to Honiara to take advantage of the infrastructure left behind by the U.S. military.