The German assault on Poland began at 4:45 am on September 1, 1939. The Polish air force, dispersed prior to the invasion, instead of rising en masse to challenge the Luftwaffe, saw its numbers quickly whittled down in a misguided hope to preserve its striking power. The Polish army fought mostly alone, while German planes pounded the Polish capital. Within just two weeks, German artillery and airpower had killed over 60,000 of Warsaw's citizens.

Japan and the Soviet Union clashed repeatedly late in the 1930s most notably in 1938 near the Soviet port of Vladivostok, and then again in a massive battle in 1939 on the Soviet controlled Mongolian border at Khalkin Gol - Nomonhan. At Khalkin Gol the Red Army decisively defeated Japan, ultimately causing the Japanese to abandon plans for invading Siberia with up to 45 infantry divisions.