On 1 April 1937, Burma became a separately administered colony of Great Britain, and Ba Maw became the first Prime Minister and Premier of Burma. Ba Maw was an outspoken advocate for Burmese self-rule, and he opposed the participation of Great Britain, and by extension Burma, in World War II. He resigned from the Legislative Assembly and was arrested for sedition. In 1940, before Japan formally entered the war, Aung San formed the Burma Independence Army in Japan.