This two-part PBS documentary explores the war between Mexico and the United States which changed a continent. This first part studies the America in the 1820s, as Mexico recovers from its war of independence and the United States rapidly expands its ter ritory. Texas breaks free from Mexico in 1836, and in 1846 U.S. and Mexican troops clash in a border dispute. War begins. Directed by Ginny Martin; narrated by Bruce DuBose. Closed captioned.