Before the summer of 1942 the United States fought a defensive war in the Philippines. The change in strategy, was when the U.S. went on a land offensive to defeat the Japanese. They planned to do this by capturing all the islands until their empire was nothing but their Japan itself. The name of the battle that marked the turning point was the Battle of Guadalcanal. Japanese forces reached Guadalcanal in May of 1942. When the Allies noticed construction of an airfield on Guadalcanal, the U.S. did an amphibious landing, and the two forces went back and forth. It became a major turning-point in the war because it stopped Japanese expansion.