Question

The foreign power was able to invade Mexico successfully because the U.S. was engaged in its own _____________________.

Answer 1

The foreign power here refers to France, which invated Mexico in 1861, and it established Mexico's only coronated head: Emperor Maximilian (brother of Austria's Franz Joseph).

The U.S. could not intervene at the time as it was engaged in its own Civil War (1861-1865).