Japan became part of World War II when it invaded China in 1937, which many historians consider the true beginning of World War II in Asia. Here’s a breakdown of key events:
🗓️ Timeline of Japan’s Entry into WWII:
July 7, 1937 – Second Sino-Japanese War Begins
- Japan launched a full-scale invasion of China after the Marco Polo Bridge Incident.
- This marked Japan’s major military expansion and is often considered the start of WWII in Asia.
September 27, 1940 – Japan Joins Axis Powers
- Japan signed the Tripartite Pact with Germany and Italy, formally entering into a military alliance.

December 7, 1941 – Attack on Pearl Harbor
- Japan bombed Pearl Harbor, Hawaii, leading the United States to declare war on Japan the next day.
- This brought WWII into a truly global conflict involving both the Pacific and European theaters.
🌏 Summary:
- 1937: Japan begins aggressive expansion in Asia (WWII begins in Asia).
- 1940: Official alliance with Axis powers.
- 1941: Attack on Pearl Harbor brings Japan fully into WWII as a global war.