Americans have never fully grasped why Brexit — Britain’s exit from the European Union — matters to them. That’s made it easy for the EU’s friends to lump Brexit together with President Donald Trump as symbols of all that’s wrong with the West today.

The truth is that Brexit shows what’s right with it.

If you follow Brexit casually, you might think the British public is having second thoughts about leaving the European Union. Not so. Britain is still pretty much where it was when it voted to leave in June 2016. The only big difference is that, as Britain did vote to leave, a substantial majority wants to get on with the job.

The latest poll from YouGov — which got the 2017 British election right — shows 45 percent believe that, in hindsight, Britain was wrong to leave; 42 percent think it was right. But when you ask what Britain should do today, only 31 percent of the public want to stop Brexit or even have a second referendum.

Since the EU referendum, we’ve learned a lot about why people voted as they did. Some results were more unexpected than others — such as those in the southern valleys of Wales.

The valleys are bastions of the left-wing Labor Party, which in Wales opposed Brexit almost unanimously. They have a strong Welsh identity; Brexit was supposedly an English cause. Yet the valleys voted for Brexit, often emphatically.

Why? Researchers from Cardiff University in Wales found that valley voters didn’t think the EU had benefited Wales. The voters believed the EU spent too much money on vanity projects.

The voters also feared Polish immigration was driving down wages. These are left-wing, working-class people, not xenophobes. They believed immigration was good for companies, not for the Welsh people.

There’s nothing new in this belief. It was the working-class argument against the EU for decades.

What’s new is the rise of the elite left, which dominates the Labor Party as it does the Democratic Party. That urban, prosperous left values multiculturalism as a good in itself. It therefore likes immigration, and sees the EU as a way to promote it.

And that’s one reason Brexit matters to the United States. There’s a lot of discontent in the Welsh valleys, and in the West as a whole. The EU’s response — and the response of the urban elite — to that discontent is to ignore it, to ridicule it or to blame it on the Russians. And it’s to reinforce the status quo.

But the discontent exists. Praising the status quo is no answer. Brexit is a positive way to show that change is possible. Britain’s not turning inward. It’s seeking free trade deals around the world. It’s as committed as ever to NATO. It is breaking the status quo, but in a responsible way.

Yet Brexit wasn’t caused by postmillennial anxieties. British opinion on the EU hasn’t moved much since 1994. What happened in 2016 wasn’t the rise of populism. It was that the British people were finally given a chance to vote on whether they wanted to be in the EU.

And that’s the other reason Brexit matters to the United States. The case for Brexit is simple: Democracies shouldn’t do things that are persistently unpopular with the public. The right to control the government rests with the people, not faraway bureaucrats.

Today, Britain is legally subordinate to the EU. Contrast that with the United States. I like Mexico and Canada as neighbors. I want to cooperate with them. I just don’t want to form a union with them.

If the EU is right, the only way we can cooperate with other nations is to give up our right to control our own affairs. That’s not cooperation. It’s subordination. And if you think the West has a populist problem now, wait until you see what happens when you tell people their votes just don’t matter.