In 1953 the CIA lead a coup against Iran's democratically-elected prime minister, Mohammad Mosaddeq. In his place America and Britain helped install a king. That regime came crashing down in 1979, and Iran has been suspicious of America ever since. The United States subsequently supported Iraq during the Iran-Iraq War, providing both intelligence and arms to Saddam Hussein. Interestingly, Iraq's brutal dictator turned out to be a brutal dictator. We went to war with him during the early 90s and again in 2003. To the great surprise of the Bush administration, ousting the strongman has not transformed Iraq into a liberal democracy.
Similarly, when Nobel Peace Prize recipient Barack Obama bombed Libya to oust Muammar Gaddafi, the vacuum of power invited more strife and violence.