The U.S. airstrike that killed a prominent Iranian general in Baghdad raises tensions even higher between Tehran and Washington, after months of trading attacks and threats across the wider Middle East. 

How Iran will respond remains in question as well, though its supreme leader warned that a "harsh retaliation is waiting" for those who killed Revolutionary Guard Maj. Gen. Qassem Soleimani early Friday morning. That could include anything, from challenging U.S. warships in the Persian Gulf, firing ballistic missiles or deploying the asymmetrical proxy forces Iran has cultivated to cover for its long-sanctioned conventional forces. 

Soleimani's death is the latest in a series of escalating incidents traces back to President Donald Trump's decision in 2018 to unilaterally withdraw America from Iran's nuclear deal with world powers. However, overall enmity between Iran and the U.S. date back to its 1979 Islamic Revolution, as well as a 1953 U.S.-backed coup in Tehran that cemented the power of its ruling shah over an elected prime minister. 

Here's where things stand now:

THE GENERAL'S KILLING

A U.S. airstrike near Baghdad's international airport killed Soleimani, 62, as well as Abu Mahdi al-Muhandis, the deputy commander of Iran-backed militias in Iraq known as the Popular Mobilization Forces, and five others. The Defense Department said it killed Soleimani because he "was actively developing plans to attack American diplomats and service members in Iraq and throughout the region." It also accused Soleimani of approving the attacks on the U.S. Embassy in Baghdad earlier this week. Soleimani led the paramilitary Revolutionary Guard's Quds, or Jerusalem, Force.  That included overseeing forces fighting in Syria, as well as militias that targeted U.S. forces in Iraq with deadly bomb attacks after the 2003 invasion that toppled Saddam Hussein. 

MONTHS OF ATTACKS

Citing an unspecified threat from Iran, the White House in May ordered a U.S. aircraft carrier to rush to the Persian Gulf. Soon after, explosions the U.S. blames on Iranian-laid mines targeting oil tankers near the crucial Strait of Hormuz, through which 20% of all oil passes. Iran denied being involved, though it did seize oil tankers in response to one of its tankers being seized off Gibraltar. Iran also shot down a U.S. military surveillance drone. Trump pulled back from retaliating for the attack. Meanwhile, attacks on Saudi Arabia's energy industry escalated to a missile-and-drone strike in September temporarily halving its oil production. Israel meanwhile has repeatedly struck Iran-linked targets in Syria in recent years and has warned against any permanent Iranian presence on the frontier. The attacks culminated with American airstrikes hitting Iranian-backed militias in Iraq and those  militiamen attacking the U.S. Embassy in Baghdad.

IRAN'S FALTERING NUCLEAR DEAL

The attacks came after Trump's decision in May 2018 to withdraw America from Iran's nuclear deal with world powers. The 2015 accord saw Iran agree to limit its enrichment of uranium in exchange for the lifting of economic sanctions. Trump re-imposed American sanctions and levied even harsher ones, crippling its crucial oil industry. Iran initially proposed a policy called "strategic patience," hoping to wait Trump out. But as Europe largely hasn't been able to offer Tehran  a way around American sanctions, Iran has begun taking steps away from the deal. That has included breaking enrichment, stockpile and centrifuge limitations, as well as restarting its program at an underground facility. Tehran appears poised to take a new step away from the deal beginning from Sunday.

IRAN'S MEANS OF RETALIATION

Iran's conventional military force is limited. The backbone of its air power remains pre-revolution American F-4s, F-5s and F-14s, with a mix of other Soviet, French and aging aircraft. That fleet is outgunned by the modern U.S.-supplied fighter jets flown by Israel and the Gulf Arab states. To counter that, Iran has put much of its money toward developing a ballistic missile program operated by the Guard. Iran could fall back on its regional militant allies or proxies to launch an attack, like Iraqi militiamen, Lebanon's Hezbollah or Yemen's Houthi rebels. The U.S. has blamed car bombs and kidnappings never claimed by Iran on Tehran as well. The Guard also routinely harasses U.S. Navy vessels in Persian Gulf and surrounding waterways, while Iran has surface-to-sea missile batteries along its coast as well. 

AMERICA'S BROAD MIDEAST PRESENCE

The Persian Gulf hosts a series of major American military installations. The U.S. Navy's 5th Fleet, which oversees the region, is based in Bahrain, an island nation off the coast of Saudi Arabia that is home to over 7,000 American troops. Kuwait hosts over 13,000 American troops and the U.S. Army's Central forward headquarters. Dubai in the United Arab Emirates is the largest port of call for the U.S. Navy outside of America. The UAE hosts 5,000 U.S. military personnel, many at Abu Dhabi's Al-Dhafra Air Base, where American drones and advanced F-35 jetfighters are stationed. The forward headquarters of the U.S. military's Central Command is at Qatar's sprawling Al-Udeid Air Base, home to some 10,000 American troops. In Oman, the sultanate allows thousands of overflights and hundreds of landings a year, while also granting access to ports and its bases. Meanwhile, U.S. forces are in Afghanistan, Iraq and Syria. 

A HISTORY OF ENMITY

Tensions between Iran and the U.S. trace back decades. For Iranians, they point to the 1953 CIA-backed coup that toppled Mohammad Mosaddegh and cemented the power of Shah Mohammad Reza Pahlavi. Pahlavi served as a key U.S. ally for decades after, buying billions of dollars of weapons and allowing America to spy on the Soviet Union from his country. Over time, however, he eliminated all political opposition and seized all power in the country. By 1979, the fatally ill shah fled the country. The 1979 Islamic Revolution and the hostage crisis soon followed, a history the two countries remain captive to until today.

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