Who were the main opponents of the state of Iran?

Depends on the period. After the Islamic revolution of 1979, the main opponents of Iran are Iraq (they fought with it in the 1980s) and the United States, which put pressure on Iran in every way (sanctions, information war, etc.).

In the 19th century, the opponents of Iran were Russia and England, they essentially divided it into spheres of influence.

In the XVI-XVIII centuries, his main opponents were:

Ottoman Empire. She successfully fought with Iran in the 16th century, but under Shah Abbas, the Persians managed to take revenge (by the beginning of the 17th century).
The Portuguese, they were competitors on the Indian Ocean trade routes.
Pashtun tribes fought with him in the 18th century.
Until that time, Iran (Persia) had to fight with Byzantium and the Mongol state.