Japan joins Britain after the fall of France

What could Japan gain by joining Britain after the fall of France if it had not invaded China?

It could obtain close wartime cooperation and favorable deals while its fleet transformed the Mediterranean balance without the historical sanctions crisis.

Britain might offer no formal concessions simply for Japan's promise to enter the war. Actual participation could nevertheless bring favourable deals and close cooperation. Without the 1937 invasion of China, the historical sanctions would not apply in the same way. Japanese naval participation could free British forces in the Indian Ocean and bring Kongos or carriers into the Mediterranean. A joint British, Australian, and Japanese force at Cape Matapan illustrates the possible effect.