The U.S. was involved in a minor concurrent conflict during the war, although they ignored the UK's offer of alliance and did not coordinate with the Anglo-French forces. In 1856, the Chinese garrison at Canton shelled a United States Navy steamer; the U.S. Navy retaliated in the Battle of the Pearl River Forts. The ships bombarded then attacked the river forts near Canton, taking them. Diplomatic efforts were renewed afterward, and the American and Chinese governments signed an agreement for U.S. neutrality in the Second Opium War.