 The African slave trade became illegal on January 1, 1808.By 1807 the tonnage registered in the United States engaged in foreign trade had increased to 848,307.The United States declared war on Britain on June 18, 1812, for a combination of reasons—outrage at the impressment (seizure) of thousands of American sailors, frustration at British restrictions on neutral trade while Britain warred with France, and anger at British military support for hostile tribes in the Ohio-Indiana-Michigan area.