Multiple choice The Mexican-American War was the first time a U.S. conflict was fought mostly... on foreign soil. on national soil. with the help of the French. with the help of the British. Reveal answer Fill a bubble to check yourself A Correct answer Explanation The Mexican-American War (1846-1848) marked the first time in U.S. history that American military forces fought a major conflict primarily on foreign soil, invading and occupying parts of Mexico.