During the early 20th century, particularly during World War II, Japan expanded its military presence across Asia. This included the invasion of China in 1937, which led to widespread atrocities such as the Nanjing Massacre. Japan sought to establish a greater East Asia co-prosperity sphere, aiming to dominate the region economically and politically. In 1941, Japan attacked the United States at Pearl Harbor, prompting the U.S. to enter the war. Throughout the conflict, Japan occupied several territories, including parts of Southeast Asia and the Philippines. The war ended in 1945 after Japan's surrender following the atomic bombings of Hiroshima and Nagasaki.