Even by the Middle Eastern standards, the past year has been full of surprises. A bolt-from-the-blue attack by Hamas produced the deadliest day for Jews since the Holocaust. The resulting Israel-Hamas war in Gaza has now lasted longer than nearly anyone first imagined. Iran launched perhaps the largest drone and missile strike in history against Israel, which was blunted by unprecedented cooperation from countries in the region and beyond.

Yet the biggest surprise is also the most ominous for global order. A radical, quasi-state actor most Americans had never heard of, the Houthis of Yemen, have mounted the gravest challenge to freedom of the seas in decades — and arguably beaten a weary superpower along the way.

The Houthis began their campaign against shipping through the Bab el-Mandeb, which connects the Red Sea and Gulf of Aden, in late 2023. They are nominally attacking out of sympathy for the Palestinian people, but also to gain stature within the so-called Axis of Resistance, a group of Middle Eastern proxies cultivated by Iran.

In January, Washington responded with Operation Prosperity Guardian, which features defensive efforts (largely by U.S. destroyers) to shield shipping from drones and missiles, and also airstrikes against Houthi attack capabilities within Yemen. The results have been middling at best.

The Houthis have cut Suez Canal traffic by more than half, starving Egypt of toll revenues. They have bankrupted the Israeli port of Eilat in the Gulf of Aqaba. Nearly a year on, the group appears less deterred than emboldened: It recently crippled an oil tanker, threatening a spill with catastrophic environmental consequences. A waterway that carried 10% to 15% of global trade has become a killing zone.

This saga combines dynamics old and new. The Bab el-Mandeb, Arabic for “gate of tears,” has long been a locus of struggle. This chokepoint is surrounded by instability in the southern Arabian Peninsula and Horn of Africa. That situation has invited conflict and foreign intervention for decades, but the Houthis’ campaign also displays newer global troubles.

One is the falling cost of power-projection. The Houthis aren’t a traditional military juggernaut; they don’t even fully control Yemen. Yet they have employed drones and missiles to control access to vital seas.

The Houthis have had help in doing so: Iran has provided weapons and the know-how needed to manufacture them. But the Red Sea crisis still shows how seemingly minor actors can use relatively cheap capabilities to extend their destructive reach.

The second feature is strategic synergy among U.S. foes. The Houthis became more fearsome thanks to mentorship by Iran and Hezbollah. Since October 2023, they have allowed most of China’s shipping to pass without harm. The Houthis have also received encouragement — and, it seems, direct support — from a Russia that is eager to exact vengeance on Washington.

Beijing and Moscow reap geopolitical rewards when America is burdened by Middle Eastern conflicts, so both are willing to let this crisis fester, or even make it worse.

Further inflaming matters is a third factor: America’s aversion to escalation, which is rooted in military overstretch. A global superpower has been reduced to an inconclusive tit-for-tat with a band of Yemeni extremists. It is an evasion to claim that this very extremism makes the Houthis “undeterrable.”

The core issue is that Washington has hesitated to take stronger measures — such as sinking the Iranian intelligence ship that supports the Houthis, or targeting the infrastructure that sustains their rule within Yemen — for fear of inflaming a tense regional situation.

That approach has limited the near-term risk of escalation, but allowed Tehran and the Houthis to keep the showdown simmering at their preferred temperature. It also reflects the underlying fatigue of a U.S. military that lacks enough cruise missiles, laser-guided bombs, strike aircraft and warships to prosecute the campaign more aggressively without compromising its readiness for conflicts elsewhere.

Thus a fourth feature: The rotting of norms the international community has taken for granted. The global commercial damage caused by the Houthis has actually been limited, thanks to the adaptability of the shipping networks that underpin the world economy. But the precedent is awful: The Houthis have upended freedom of the seas in a crucial area and paid a very modest price.

Russia’s war in Ukraine is simultaneously stressing another bedrock principle, the norm against forcible conquest. Revisionist actors are challenging the global rules that underpin the relative affluence, security and stability of our post-1945 world.

A dramatic course correction by the U.S. probably isn’t imminent. President Joe Biden is still chasing that elusive Israel-Hamas cease-fire; this would at least deprive the Houthis and other Iranian proxies of their pretext for violence, even if no one is really sure whether it would end the Red Sea shipping attacks. He hopes to get through the presidential elections without more trouble with Tehran.

But this muddle-through approach may not survive for long after that. Whoever becomes president in 2025 will have to face the fact that America is losing the struggle for the Red Sea, with all the pernicious global implications that may follow.

Hal Brands is a Bloomberg Opinion columnist and the Henry Kissinger Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies. He is also a senior fellow at the American Enterprise Institute, the co-author of “Danger Zone: The Coming Conflict with China,” a member of the State Department’s Foreign Affairs Policy Board, and a senior adviser to Macro Advisory Partners. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.