The two causes of you Mexican American War was slave state and the treaty of velasco.
The Battle of the Little Bighorn, fought on June 25, 1876, near the Little Bighorn River in Montana Territory, pitted federal troops led by Lieutenant Colonel George Armstrong Custer (1839-76) against a band of Lakota Sioux and Cheyenne warriors. Tensions between the two groups had been rising since the discovery of gold on Native American lands. When a number of tribes missed a federal deadline to move to reservations, the U.S. Army, including Custer and his 7th Calvary, was dispatched to confront them.
The purpose of the Monroe Doctrine was to C) warn European nations not to form new colonies in the Americas. The goal was to establish American hegemony in the Western Hemisphere.
This would be the Rhine RIver