Onetime allies, the United States and Iran have seen tensions escalate repeatedly in the four decades since the Islamic Revolution.

The Democratic Republic of Congo has been subjected to centuries of international intervention by European powers, as well as its African neighbors. This timeline traces the role of the outside forces that have beleaguered eastern Congo since the end of the colonial era.

The United States and China have one of the world’s most important and complex bilateral relationships. Since 1949, the countries have experienced periods of both tension and cooperation over issues …

Since India’s independence, ties with the United States have weathered Cold War–era distrust and estrangement over India’s nuclear program. Relations have warmed in recent years and cooperation has strengthened across a range of economic and political areas.

The International Olympic Committee says the games are not meant to be political. But governments and athletes have frequently used the Olympics to make statements through boycotts and protests.