U.S.-Iran relations have been increasingly tense since Donald Trump took office, but the president’s decision to kill Maj. Gen. Qasem Soleimani has led the U.S. and Iranian governments to inch closer to war than ever before — Iran reportedly retaliated by striking multiple Iraqi bases housing U.S. troops early Wednesday. The growing conflict has ramifications for the entire Middle East. But none of it was inevitable. In fact, Iranians once saw Americans as friends, and the two nations became close allies by the mid-20th century.

Although the Islamic Republic of Iran has not been blameless for worsening relations since its creation in 1979, the United States bears most of the blame for the two nations’ dramatic transformation from allies into enemies.

The United States and Iran had their first diplomatic encounters in the 1850s, which led to a treaty of friendship. The nations’ relationship remained friendly but distant through the early 20th century. Multiple times in the late 1800s and early 1900s, Iran requested U.S. assistance in fending off Britain’s and Russia’s increasing attempts to dominate Iranian affairs. Yet before World War II, the United States declined, following a policy of strict neutrality and noninvolvement in Iran’s internal affairs. Nonetheless, the U.S. government worked to maintain friendly relations, built closer economic ties and supported the activities of U.S. citizens and businesses in Iran.

Despite the U.S. government’s aloofness, Iranians developed a generally positive view of the United States and Americans. The American Revolution offered inspiration for Iranian nationalists, and the United States had not attempted to dominate Iran, unlike Russia and Great Britain. U.S. citizens also fostered goodwill in Iran: American Protestant missionaries built hospitals and schools across Iran that provided much-appreciated services, and missionary doctors provided medical services to Iran’s royal family.