The primary cause of the War of 1812 between the United States and Great Britain was maritime conflict, particularly British restrictions on American trade and the impressment of American sailors into the Royal Navy. Tensions escalated as the British sought to control trade with France, particularly during the Napoleonic Wars, significantly affecting American merchant shipping. The U.S. also faced issues related to British support for Native American resistance against American expansion in the Northwest Territory. These grievances collectively fueled growing resentment and ultimately led Congress to declare war on Britain in June 1812, marking a significant conflict in early American history.