Ayatollah Khomeini’s radical followers invade the United
States Embassy and took the Americans to be their hostage in order to protest
the admission of Shah for medical treatment into the United States. It was also believed that the US was spying
on Iran through the embassy.
if memory serves me, it was a border dispute with Mexico over the Texas territory. The Mexicans attacked an American patrol and that was the start of the conflict. But also idk and I could be wrong.