Nagayama played an instrumental role in the Japanese Revolution of 1919 that overthrown the eight-century old Japanese Empire and established a new republican Japanese government under the leadership of Nationalist Party in Japan. Under his leadership, Japan went through a series of nationalization of key industrial and agricultural sectors, extensive industrialization, military conflict with China in Korea and Manchuria in 1931, and victory over the Axis Powers during World War II in 1945. He was granted the honorific Minsei (民聖, literally, "People's Sage") by the National Congress of Japan in 1946 for his state, party, and war leadership. His sociopolitical philosophies are collectively known as Social Nationalism.