4 things that secured and created Americas borders were The Louisiana Purchase, Convention of 1818, Adams-Onis Treaty and Webster-Ashburton Treaty. TheLouisiana Purchase was when America bought All the land from west of Louisiana to the Rocky Mountains for 15 million dollars from France. The Adams-Onis treaty purchased Florida from Spain and secured a border from Rocky Mountains to Pacific Ocean. The Webster-Ashburton Treaty resolved border issues between U.S and British North American colonies. The Convention of 1818 was signed by America and Britain to secure a border between Canada and America.