The bloody mess that is Syria stands as Exhibit A of what is happening to global order with the retreat of American leadership. The carefully circumscribed strike ordered by President Donald Trump last week will do nothing to change the reality that he, like Barack Obama before him, has left a power vacuum in the heart of the Middle East. The beneficiaries are Russia, Iran, Hezbollah, Turkey and a host of jihadists who will haunt the region — and the West — long after the end of the Islamic State.

That’s the obvious story. What’s less evident is how far-reaching and consequential the collapse of American-led order has been in the 15 months since Trump took office. In multiple miserable corners of the world, where U.S. envoys and aid would normally be helping victims, deterring malevolent actors and seeking political solutions, there is a void.

Let’s take a tour. Start with the Western Hemisphere, whose leaders last week convened at the eighth Summit of the Americas since 1994 - and the first not attended by the U.S. president. The region is watching one of the biggest crises it has experienced in modern times: the political and economic implosion of Venezuela, which has inflicted violence and hunger on tens of millions of people and caused more than 1 million to flee the country- the largest displacement of people in Latin American history.

For a century and more, Latin American and Caribbean countries in crisis could expect that the United States would intervene - for better or perhaps for worse - to break their fall. The summit offered a chance for Washington to rally its allies behind a concerted strategy for the refugees and for the autocratic regime in Caracas.

Except Trump was not there. In his only effort to address the crisis with regional leaders, at a dinner last September, he foolishly raised the idea of military intervention. He has since ignored suggestions by some of the leaders for more realistic measures, such asan embargo on Venezuelan oil. The senior State Department positions for Latin America and for refugee affairs have not been filled. Venezuela’s downward spiral will continue.

Next stop: South Sudan, a country that came into existence in 2011 largely thanks to U.S. diplomacy. About two years later, a civil war erupted between rival factions, and it has persisted ever since. Tens of thousands have been killed and more than 2 million driven out of the country; since last year the United Nations has said South Sudan is on the brink of famine.

The robust American stewardship across two administrations has disappeared. The State Department used to have a special envoy for South Sudan; the post is vacant. The only senior Trump administration official to show an interest in the country is U.N. Ambassador Nikki Haley, who visited in October and who has pushed the U.N. Security Council — unsuccessfully — to impose an arms embargo. Both George W. Bush and Obama took a personal interest in South Sudan. Trump, needless to say, has not.

Next, Myanmar, another nation transformed by U.S. diplomacy. In an effort to free itself from comprehensive U.S. economic sanctions and gain some independence from China, the country’s military regime freed Nobel Peace Prize winner Aung San Suu Kyi from prison and then allowed a relatively free election in 2015. Obama visited the country, also called Byrma, twice. Then, last August, the generals embarked on a brutal campaign against the Rohingya minority, driving nearly 700,000 people across the border into Bangladesh.

Belatedly, then-Secretary of State Rex Tillerson called the campaign what it was, ethnic cleansing. But the U.S. response to this staggering atrocity has been anemic. Under pressure from Congress, one general in charge of the campaign was sanctioned and some visa restrictions were applied to others. But again, the only senior official to engage was Haley, who has pressed for a U.N. special envoy. Forget about an American envoy: Even the senior State Department post for the region has, as elsewhere, no permanent appointee.

A final stop is worthwhile, somewhere near Tibet, the Chinese-ruled land that has become a laboratory for high-tech, 21st-centuryrepression. The prime minister of the Tibetan government-in-exile, Lobsang Sangay, was in Washington last week for a singular purpose: to try to persuade the Trump administration to fill the State Department post of special coordinator for Tibetanissues - which, of course, is vacant.

It might seem like a small bureaucratic function, but as Sangay pointed out, no other government in the world has a Tibet coordinator. This U.S. official, he said, has been vital in getting other countries to attend meetings with his government, in channeling aid and in simply forcing China to address Tibet. Without the U.S. representative, he said, “the Tibet issue is not raised.” A little-noticed loss, perhaps, but one of many in a world without U.S. leadership.

Jackson Diehl is deputy editorial page editor of The Post. He is an editorial writer specializing in foreign affairs.