Could either japan or Germany have successfully invaded America?

It is highly unlikely that either Japan or Germany could have successfully invaded the United States during World War II. Several factors contributed to this unlikelihood:

Geographic Separation: The United States is separated from both Japan and Germany by vast stretches of ocean. Invading the United States would have required these countries to establish and maintain naval dominance across the Pacific or Atlantic Oceans, a challenging and perilous undertaking. Japan's attempt to establish such control at Pearl Harbor failed, further diminishing the chance of a successful invasion.

Industrial and Economic Might: The United States possessed a vastly superior industrial and economic base compared to both Japan and Germany. This disparity allowed the U.S. to outproduce its wartime adversaries in weaponry, ships, aircraft, and other vital war materials. In comparison, Japan faced resource shortages and limited industrial capacity while Germany's war economy faced significant disruption from Allied bombing campaigns.

U.S. Military Strength: The United States invested heavily in building up its military strength following its experience in World War I. By the late stages of World War II, the U.S. had assembled the world's strongest and best-equipped navy, as well as large, highly trained, and well-supplied army and air forces.

Allied Support: The United States was not fighting alone. It had formidable allies in the United Kingdom, France, and the Soviet Union, sharing resources, military intelligence, and strategic support. Japan and Germany were, conversely, fighting virtually alone.

Considering these factors, and the difficulties encountered by Japan and Germany in their other military campaigns during World War II, a successful invasion of the United States appears unrealistic.