Japan joins Germany in September 1939

What happens if Japan attacks British and French Far Eastern possessions in September 1939?

The attack likely brings the United States into the war immediately, while Germany's tiny operational surface fleet does little to stop Britain sending forces east unless Italy also enters.

Germany had only Scharnhorst and Gneisenau, both still working through trials and modifications, so its surface fleet was not the chief constraint on British deployment. Britain and France still had their full Far Eastern garrisons, while Japan lacked the later forward bases in French Indochina. Attacking British and French possessions would also require Japan to move past the Philippines and probably bring the United States into the conflict immediately. Italy's six battleships mattered more to Mediterranean force allocation, and visible American entry in 1939 might persuade Mussolini to remain neutral. The resulting coalition is therefore more dangerous to Japan and Germany than the early attack is to Britain.