HELPPP PLZZZZ....What caused Louisiana and the United States to go to war with Great Britain in 1812? Britain continued to impress American sailors and violate American shipping rights during its war with France. Britain objected to the United States' purchase of Louisiana and moved troops south from Canada to oppose the agreement. British troops occupying Spanish Texas made repeated threatening demonstrations against Louisiana. Great Britain demanded the right to access and navigate the Mississippi River to reach its colonies in Canada.