1. Why are the United States and Iran at odds?
Iran was a close ally of the United States during most of the reign of Shah Mohammad Reza Pahlavi. But Pahlavi was overthrown by the 1979 Iranian revolution and replaced with a Shiite-led Islamic Republic. That November Iranian militants and took about 70 Americans hostage at the US Embassy in Tehran. The hostages were held for 444 days. Iran’s relationship with the United States rapidly deteriorated and has remained strained since.
Some point to US meddling in the Middle East and alliance with Israel and rival Sunni powers as justification for Iranian suspicions, while others argue that Iran itself is an expansionist power, eager to push the influence of the Shiite branch of Islam across the Middle East. Washington and its allies in the Middle East also suspect that Iran is seeking to develop a nuclear weapons program.
2. Why are both the United States and Iran interested in Iraq?
Iraq is Iran’s neighbor. The two nations share a 900-mile-long border. Roughly 70 percent of its population is Shiite, with most of the remaining population Sunni (in Iran, more than 90 percent of the population is Shiite), though Iran has almost four times the territory as Iraq.
In the modern era, the two countries have had a tense relationship: Iraqi dictator Saddam Hussein invaded Iran in 1980, prompting an eight-year-long war that left hundreds of thousands dead. However, after Saddam’s Sunni-dominated government was toppled by the US-led invasion of Iraq in 2003, Iraq came to be dominated by Shiite political groups, some of whom were allied with Iran.
The invasion of Iraq in 2003 ousted Saddam, but US troops remained in the country to combat a violent insurgency.
3. What effect did the rise of the Islamic State in Syria and Iraq have on the US-Iran relationship?
The Islamic State has its origins in Iraq, but it came to prominence in the chaos in the war in neighboring Syria that began in 2013 and is still ongoing. At its peak in late 2014, the self-proclaimed caliphate controlled an area the size of Britain and used it as a base to call for attacks on both US and Iranian interests.
Iran and the United States were backing opposing sides in the Syrian war. Tehran viewed Syrian President Bashar al-Assad as a key ally in the region, whereas the United States and other Western powers had backed rebels who opposed his government. But for both, the Islamic State presented a more pressing problem.
With US airstrikes, and the intervention of forces loyal to Iran and the Russian military, the Islamic State ceded the last of its territory earlier this year. However, the end of that fight raised the possibility of new conflict between Iran and the United States.
The tension between the United States and Iran was especially noteworthy in Iraq, where about 5,000 US troops are deployed ostensibly to aid the Iraqi fight against the Islamic State.
4. What relationship does Iran have with groups in Iraq and Syria?
Iran has long been accused of running a network of proxies across the Middle East, using Shiite militias and political parties to undermine rival governments. In Iraq, there are a variety of Shiite militias. They do not have identical interests, but they have had increasing political clout since the battle against the Islamic State, gaining almost a third of seats of Iraq’s parliament in 2018 elections.
Over the past year, rocket attacks on bases used by US troops in Iraq have led to increasing tension. After the strikes against Kataib Hezbollah Sunday, a senior US State Department official had briefed reporters that the blame lay not just with Iran, but also with Iraq. ‘‘It is their responsibility to protect us, and they have not taken appropriate steps to do so,’’ the official said.
5. How has President Trump changed the relationship with Iran and Iraq?
Trump viewed the Obama-era nuclear deal with Iran with suspicion and argued that the previous administration had not done enough to curtail Iranian influence across the region.
The president pulled the United States out of the deal in May 2018 and reimposed sanctions on Iran.
Tensions between the United States and Iraq have escalated. In early 2019, Iraq’s President Barham Salih said his country would reject Trump’s idea that the United States could keep American troops in Iraq to ‘‘watch’’ Iran.
Iraqis argued the airstrikes were an affront to their nation’s sovereignty and broke the status of forces agreement that allows US troops in Iraq.