This article explores the various eras in Japan's history to determine which one was the bloodiest. The Sengoku Period (1467-1615) is considered to be the bloodiest, with an estimated 4 million people dying during this time. Other wars such as the Boshin War (1868-1869) and Russo-Japanese War (1904-1905) resulted in an estimated 150,000 and 600,000 casualties respectively. However, World War II (1939-1945) was undoubtedly the bloodiest period in Japanese history, with an estimated 4 million deaths on both sides combined.