The entry of the USA into the war with Japan at the end of 1941 led to the receipt of Lend-Lease equipment from the United States, including aircraft. American Lend-Lease aviation equipment had already begun to arrive in China as early as the middle of 1941, though that includes the first shipments before January 1942 which arrived under the guise of purchases. Including previously purchased American aircraft, US soon replaced USSR as the largest supplier for the Chinese Nationalist air force during the war (Including the Second Sino-Japanese War that actually broke out in 1931 when Japan invaded Manchuria).