Breaking the Outer Ring:

By the beginning of 1944, United States Marine forces had already
made a dramatic start on the conquest of areas overrun by the Japanese early
in World War II. Successful American assaults in the Southwest Pacific
beginning with Guadalcanal in the Solomon Islands in August 1942, and
in the Central Pacific at Tarawa in the Gilbert Islands in November 1943,
were crucial campaigns to mark the turn of the Japanese floodtide of conquest.
The time had now come to take one more decisive step: assault of the islands held by Japan before 1941.