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).
Adopted and adapted the Greeks alphabet. The Romans also adopted some of the Greeks gods. Adopting Greeks medicine and sports, the Romans literature was based on Greeks tragedies and comedies.