The oil route that could be at the center of a U.S. warning of 'unrelenting force' against Iran

After what national security adviser John Bolton called "a number of troubling and escalatory indications and warnings," the U.S. government said Sunday that it was deploying the USS Abraham Lincoln carrier strike group and a bomber task force to the U.S. Central Command (Centcom) region.

Centcom's operational area includes the Middle East and Central Asia, but Bolton's statement indicated that U.S. attention was primarily focused on one country: Iran.

The move's intended message, Bolton said, was to send a "clear and unmistakable message to the Iranian regime that any attack on United States interests or on those of our allies will be met with unrelenting force."

It was not immediately clear what prompted concerns over an Iranian attack.

After withdrawing from the 2015 Iran nuclear treaty, the Trump administration has put significantly more pressure on Iran in recent months by imposing sanctions on Iranian oil exports and by blacklisting Iran's Revolutionary Guard Corps as a terrorist organization.

While Bolton's strongly worded statement to announce additional measures over the weekend was as unusual as those previous moves, the deployment of additional U.S. resources to the region amid heightening tensions has become a more regular occurrence: The reason is the narrow stretch of water at the mouth of the Persian Gulf, the Strait of Hormuz.

Amid threats from abroad, Iran has often been quick to remind the world of its key location along one of the world's main oil tanker routes. It once again threatened to close that key transport route in recent weeks. When Bahrain, a Persian Gulf nation with a sizable U.S. troops presence, threatened that it would not allow Iran to proceed with such a move, an Iranian official responded: "Mind your small size and do not threaten someone bigger than yourself."

The Strait of Hormuz is one of the world's most crucial transport routes for oil. About a third of the world's oil tanker traffic passes through the strait, which is bordered by Iran and Oman. In 2016, 18.5 million barrels of petroleum were shipped through it every day, making it the world's single most important maritime route for many nations' oil supplies.

Theoretically, Iran could attempt to cut off the Strait of Hormuz - which connects the Persian Gulf and the Gulf of Oman - by deploying its naval vessels or laying mines, which could take months to clear. At its narrowest point, the strait's shipping route is only two miles wide. But the U.S. military has extensive footholds in the region, including the headquarters for the Navy's 5th Fleet in Bahrain.

If theStrait of Hormuz were inaccessible, the world's supply in shipped daily global oil exports would suddenly drop by about 30 percent, experts predict. Overall oil supplies would drop by about 20 percent, according to numbers compiled before the recent U.S. sanctions on Iranian oil exports took effect.

Some of the oil may be rerouted via pipelines that have been expanded over fears of an Iranian-Western clash, but those are still limited in capacity and more expensive.

As a result, oil prices would immediately spike, as Arab oil suppliers would lose their market access either entirely or to a large extent. Given the global economic repercussions, the United States and other adversaries of Iran would likely take military action. The United States would not be the only nation interested in resolving a dispute as quickly as possible, however, as the vast majority of supplies are delivered to Asian markets, in particular to Japan, India and China.

Iran has made similar threats before, for instance, in 2011, 2012, 2016 and 2018.

Some of those threats were intended to be rhetorical, at least in the short run. Last July, for instance, Iranian President Hassan Rouhani implied that Iran had the power to severely disrupt the oil trade in the Persian Gulf, which would likely have meant an attempt to blockade the Strait of Hormuz. Rouhani later appeared to repeat his veiled threat and was quoted on his official website as saying: "Mr. Trump! We are the people of dignity and guarantor of security of the waterway of the region throughout the history. Don't play with the lion's tail; you will regret it."

Trump eventually responded on Twitter, writing that Iran "WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE," in case it threatened the United States.

But prior incidents have shown how serious both nations take the Strait of Hormuz, and how easily maneuvers could escalate. In 2016, Iranian naval vessels veered close to American warships in the strait, prompting a U.S. warning. "These are incidents that carry a risk of escalation, and we don't desire any kind of escalation," Pentagon spokesman Peter Cook warned Iran at the time.

With more U.S. military assets headed into the region, the likelihood of an escalation has once again inched up.