Iran this week punctuated 10 days of naval exercises in the Strait of Hormuz and threats to close it with a warning to U.S. Navy ships to stay out of the Persian Gulf, which requires passage through the strait. The tough talk may have temporarily juiced oil prices, but it failed to impress militarily. Recent news reports have cited U.S. military officials, defense analysts, and even an anonymous Iranian official arguing that Iran likely lacks the will and ability to block shipping in the strait. That argument isn’t new: Iran’s economy depends on shipments through the strait, and the U.S. Navy can keep it open, if need be. What’s more, the Iranians might be deterred by the fear that a skirmish over the strait would give U.S. or Israeli leaders an excuse to attack their nuclear facilities.

The obviousness of Iran’s bluster suggests its weakness. Empty threats generally show desperation, not security. And Iran’s weakness is not confined to water. Though Iran is more populous and wealthier than most of its neighbors, its military isn’t equipped for conquest. Like other militaries in its region, Iran’s suffers from coup-proofing, the practice of designing a military more to prevent coups than to fight rival states. Economic problems and limited weapons-import options have also undermined its ability to modernize its military, while its rivals buy American arms.

Here’s how Eugene Gholz and Daryl Press summarize Iran’s conventional military capability:

Iran … lacks the equipment and training for major offensive ground operations. Its land forces, comprising two separate armies (the Artesh and the Islamic Revolutionary Guard Corps), are structured to prevent coups and to wage irregular warfare, not to conquer neighbors. Tehran’s air force is antiquated, and its navy is suited for harassment missions, not large amphibious operations across the Gulf. Furthermore, a successful invasion is not enough to monopolize a neighbor’s oil resources; a protracted occupation would be required. But the idea of a sustainable and protracted Persian Shi’a occupation of any Gulf Arab society—even a Shi’a-majority one like Bahrain—is far-fetched.

Despite Iran’s weakness, most U.S. political rhetoric—and more importantly, most U.S. policy—treat it as a potential regional hegemon that imperils U.S. interests. Pundits eager to bash President Obama for belatedly allowing U.S. troops to leave Iraq say it will facilitate Iran’s regional dominance. The secretary of defense, who says the war in Iraq was worth fighting, wants to station 40,000 troops in the region to keep Iran from meddling there. Even opponents of bombing Iran to prevent it from building nuclear weapons regularly opine on how to “contain” it, as if that required great effort.

Some will object to this characterization of Iran’s capabilities, claiming that asymmetric threats—missiles, the ability to harass shipping, and nasty friends on retainer in nearby states—let it punch above its military weight. But from the American perspective—a far-off power with a few discrete interests in the region—these are complications, not major problems. Our self-induced ignorance about Iran’s limited military capabilities obscures the fact that we can defend those interests against even a nuclear Iran at far lower cost than we now expend. We could do so from the sea.

The United States has two basic interests in the region. The first is to prevent oil price spikes large enough to cause economic trouble.  Although it’s not clear that an oil price shock would greatly damage the U.S. economy, we don’t want to chance it. That is why it makes sense to tell Iran that we will forcibly keep the strait open.

Iranian nuclear weapons would merely complicate our efforts to do so. For safety, both naval ships clearing mines there and tankers would want Iranian shores cleared of anti-ship cruise missiles and their radars, although doing so is probably not necessary to keep strait cargo moving. The possibility of nuclear escalation makes attacking those shore-based targets tougher. But the risk of escalation is mostly Iran’s. By attacking U.S. ships, Iran would risk annihilation or a disarming first strike. Given that, it is hard to see how nuclear weapons make closing the strait easier.

The second U.S. goal in the region is to prevent any state from gathering enough oil wealth to extort us or build a military big enough to menace us. The vastness of our military advantage over any combination of Middle Eastern states makes that fairly easy to prevent. The difficulty of Iran credibly threatening to stop exporting the chief source of its wealth makes the problem even smaller. Indeed, the odds of Iran becoming an oil super-state by conquest are so low that we probably do not need to guarantee any nearby state’s security to prevent it. For example, if Iran swallowed and magically pacified Iraq, the resulting state, while a bad thing, would create little obvious danger for American safety or commerce. Still, if we did defend Iraq’s borders, carrier-based air power along with Iraqi ground forces would probably suffice to stop Iranian columns at the border. The same goes for Kuwait and Saudi Arabia.

Because threats of nuclear attack better serve defensive goals, an Iran armed with nukes would not meaningfully change this calculus. Iran’s neighbors would not surrender their land just because Iran has nuclear weapons, if history is any guide. And U.S. guarantees of retaliatory strikes could back them up, if necessary. Nukes might embolden Iran to take chances that a state worried about invasion would not. But the difficulty of subduing a nationalistic country of 75 million people already deters our invasion.

The current contretemps with Iran is no reason for “maintaining our military presence and capabilities in the broader Middle East,” as the secretary of defense would have it. Removing U.S. forces from Iran’s flanks might strengthen the hand of the Iranian minority opposed to building nuclear weapons, though it is doubtful that alone would be enough to let them win the debate anytime soon. But even if Iran does build nuclear weapons, we can defend our limited interests in the region from off-shore.

Cross-posted from the the Skeptics at the National Interest.