Mannerheim was an officer in the Russian Army. He fought in both the Russo-Japanese War and World War I. After the Russian Revolution, Finland declared independence and Mannerheim became the Supreme Commander and regent of Finland. In 1919, he was defeated in elections and retired to private life. When the Soviets invaded Finland in 1939, Mannerheim returned to become commander of Finnish forces. He developed the "Mannerheim line", which delayed the Russian forces.
