Final answer:
The Pacific and European fronts of WWII only merged after the D-Day invasion on June 6, 1944, which was the largest amphibious invasion in history.
Step-by-step explanation:
The Pacific and European fronts of WWII only merged after the D-Day invasion. D-Day, which took place on June 6, 1944, was the largest amphibious invasion in history, with Allied forces landing on the beaches of Normandy in northern France. This invasion marked a significant turning point in the war and eventually led to the merging of the Pacific and European fronts.