As the conflict between the United States and Iran enters its sixth month under President Donald Trump, war historian and security scholar Phillips P. O'Brien — a professor of strategic studies at the University of St Andrews — argues that the outcome is now clear: the United States has lost, Iran has been empowered, and the American era of dominance in the Persian Gulf has ended.

In an analysis published Thursday on his Substack, O'Brien wrote that since World War II, the United States established itself as the dominant external security power in the region through a combination of government overthrows, massive arms sales, military bases, and extended military campaigns including the First Gulf War and the decades-long War on Terror in Afghanistan.

O'Brien pointed to the Carter Doctrine as a cornerstone of this influence. Announced during the 1980 State of the Union address in response to the Soviet invasion of Afghanistan, the doctrine declared it U.S. policy to resist any foreign power's interference with trade in and out of the Persian Gulf and committed the United States to using military force to keep the Gulf open.

"It is ironic, then, that the USA, in using military force, caused another power to close the Gulf and led to the demise of its own doctrine," O'Brien wrote.

A critical factor driving this shift, according to O'Brien, is the near-depletion of U.S. long-range precision missile stockpiles over the course of the war. As reported earlier this week, the U.S. has burned through nearly all of these munitions. O'Brien stated that as a consequence, "the USA cannot protect its forces against Iranian strike, as cheap and less advanced as that strike is compared to American capabilities."

This vulnerability has led to what O'Brien described as a precipitous withdrawal of American forces from the Persian Gulf. He cited a recent Wall Street Journal report detailing how Kuwait — a major U.S. military hub since the First Gulf War in 1991 — has been affected by the pullback. O'Brien noted that the first major Iranian attack causing mass casualties targeted a U.S. facility in Kuwait, and that the U.S. has since withdrawn many of its forces from the country.

The Wall Street Journal characterized the American withdrawal as a "rethinking" of its regional defensive posture, but O'Brien argued that the reality is starkly different: the United States has been forced to pull out rapidly because it cannot adequately protect its own forces or those of its Kuwaiti allies. This withdrawal follows months of similar reports from other facilities across the Gulf, leaving many U.S. bases reportedly empty.

For the Gulf states, O'Brien wrote, the implications are transformational. The security paradigm that for decades relied on purchasing expensive American military equipment, hosting U.S. forces, and functioning as American allies has collapsed. The shift comes against a backdrop in which regional powers had already begun diversifying their security relationships — notably with China's brokering of the Saudi-Iran diplomatic rapprochement in 2023 and Saudi Arabia's pursuit of broader strategic partnerships under its Vision 2030 framework.

"The entire security architecture that was constructed by the states in the Persian Gulf and wider Middle East will have to be entirely remade," O'Brien stated. "There are signs that they already know that. The US is showing its weakness so dramatically and in adding to that its unreliability and fickleness, is compelling the states to think more regionally."

O'Brien pointed to Saudi Arabia and Jordan as examples of states beginning to reconsider their relationships with Washington. Regional governments now perceive American partnership as a potential "strategic liability," he argued, given that the United States has demonstrated it can protect neither its own troops nor its Gulf partners.

"We need to be honest about what we have seen here," O'Brien concluded. "The U.S. is already running out of weapons, it is already pulling forces back, it is already discrediting itself. The states in the region are only acting rationally in looking at a very different future, one that relies as little as possible on the whims of a declining and fickle USA."