The 1925 Japanese invasion of the United States was a Pacific War military operation undertaken by Japanese Imperial forces in the spring and summer of 1925 in an attempt to force an early peace with the United States. With as many as 6,500,000 troops involved in the invasion, as well as over a thousand naval vessels and three thousand supporting aircraft, it was the largest single military operation in human history. Despite overwhelming numbers and early victories in California, the greater strategic goal of forcing an American capitulation was not achieved, and after the repulsion of Japanese forces in Oregon and the Colombian victory at Panama, the invasion of the United States was unsustainable and Japanese forces had withdrawn completely by the end of January 1926.