Describe the kind of war America had been fighting from December 1941 to the summer of 1942, and then describe the new strategy. Include the name of the battle that marked the turning point between the two strategies.

Before the summer of '42, the US was fighting defensively and was focused on the region of the Philippines. This was relatively successful depending on the sources, but it all changed when the US decided to implement a strategy called island hopping and go on the offense. One of the key battles here was the Battle of Guadalcanal that initiated the offensive participation of the US in the Pacific.

Credit to Greenleafable for answer