Iran's 1979 Islamic Revolution caused a rupture of relations between that country and the United States that continues today, 30 years later. However, U.S. President Barack Obama has sent signals to Tehran that dialogue may be possible, and Iran has sent its own signals to him. 

On 1 February 1979, Iran's spiritual leader Ayatollah Ruhollah Khomeini returned from exile in France. Iran's Islamic revolution had already begun, but it solidified around him.

Later that year, on 4 November, radicals scaled the wall at the U.S. embassy in Tehran and took 53 diplomats, staff, and guards hostage. Thus began 30 years of anger and confrontation, culminating in 2002 when President George Bush declared Iran to be part of the so-called "Axis of Evil," three countries he said were pursuing nuclear weapons.

"Iran aggressively pursues these weapons and exports terror, while an unelected few repress the Iranian peoples' hope for freedom," said President Bush.

But now, with the change of administration, President Barack Obama is sending a different signal. His latest message came in an interview with al-Arabiya TV. "If countries like Iran are willing to unclench their fist, they will find an extended hand from us," said President Obama.

Much of Iran's rage against the United States stems from Washington's support of Iran's Shah Mohammed Reza Pahlavi. He took control in 1953 after a CIA-backed coup against the elected Iranian government.

Many Iranians came to view the Shah as a brutal oppressor, and that bolstered Iran's Islamists, says former Iranian diplomat Shireen Tahmaseeb Hunter.

"Because of the Shah's unwillingness to offer a political atmosphere where secular political groups and so on can be active, everything therefore was left to the religious minded groups, which then used the mosques and used the other [religious] organizations to get their message across," he said.

When the United States admitted the gravely ill Shah on 22 October 1979, the rage of radicals reached the boiling point. And on 4 November, radicals seized the U.S. embassy in Tehran. And that energized an even wider group of Iranians, explained former embassy Charge d'Affairs and hostage Bruce Laingen.

"It was meant to be a symbolic, short term act," he said. "But immediately, it became something more than that. Because the very evidence of Iranian students going over the walls of the embassy inspired a passion on the streets very quickly on the part of everybody, particularly young students."

Bruce Laingen and the other hostages were held captive for 444 days until being released on 20 January 1981.

Then other events deepened the hostility. When Iraqi dictator Saddam Hussein launched in 1980 an eight-years-long war against Iran, the United States backed him. 

Then in July 1988, a U.S. Navy ship in the Persian Gulf accidentally shot down an Iranian airliner, killing all 290 people aboard.

After the U.S. toppled Saddam in 2003, Iran saw an opportunity to become influential in Iraq by working though certain clerics and political parties.

At the same time, the United States has accused Iran of providing bombs and support to Iraqi insurgents to attack American troops.

But Iran's nuclear ambitions are the main point of contention between Washington and Tehran. Iran says its nuclear program is for peaceful purposes only, but the United States and other countries believe Iran wants to build nuclear weapons. 

The United States and some Arab states believe Iran is taking these actions to establish itself as a major regional power. But the impact of that effort is downplayed by Center for Strategic and International Studies senior analyst Anthony Cordesman.

"It [Iran] is a hegemon which basically has limited influence in Iraq, has major problems with Afghanistan, can't dominate the Gulf or carry out any military action in the Gulf without provoking the United States into a response that it cannot cope with, has no great influence in Central Asia, as a power can scarcely put pressure on Turkey, and whose leverage in Syria is a much a matter of Syria using Iran as Iran using Syria," he said.

The Iranian Revolution is now 30 years old. Iranian President Mahmoud Ahmadinejad continues to make numerous demands of the United States before Tehran agrees to ease the current official diplomatic freeze. But analysts say the recent change in U.S. leadership may afford an opportunity to let go of much of the past and begin to chip away at the ice.