It can be difficult to become a U.S. citizen. A lot of people put a large amount of time, effort and money into the process of gaining an American passport or, failing that, the right to permanent residency.

But to some people, U.S. citizenship can apparently be a burden. And it's a burden that people seem to be shaking off in increasing numbers. This week, the Treasury Department released its quarterly list of individuals who had chosen to “expatriate” — i.e., renounced their U.S. citizenship or gave up their rights to permanent residence.

The list is notable for a couple of reasons. First off, Britain's Foreign Secretary Boris Johnson is on it. This means that Johnson, a dual-national who was born in New York City, has finally renounced his citizenship (as he had long promised he would). Secondly — and far more importantly in the grand scheme of things — the list shows that Johnson is just one of a total 5,411 individuals to expatriate in 2016.

As law firm Andrew Mitchel LLC noted on its blog, this was a 26 percent increase over 2015, when there were 4,279 names on the list. And it is  a 58 percent increase over 2014, when there were 3,415 names on the list. As data collected by the firm showed, while the number of individuals who expatriated from the United States had stayed pretty flat from the 1960s — and actually dipping for a while in the 1990s and early 2000s — over the past five years it has dramatically surged upward.

The number of people giving up their U.S. citizenship may in fact be higher. Ryan Dunn, a lawyer with Andrew Mitchel LLC, explained via email that his firm has suspicions that the lists released by Treasury are incomplete. However, this would not change the trend. America is seeing what is likely a historically high level of expatriation. And it seems only likely to rise further.

“Given that we’ve seen year-over-year increases in expatriation since 2012, we speculate that the trend will continue,” Dunn explained.

But why would anyone renounce their citizenship to the United States? Dunn said that in his firm's experience, it wasn't usually political. “We have not been contacted by anyone saying that they wanted to give up their citizenship because Trump won the election,” he said. Instead the motivation was simpler: money.

The United States is one of the only countries in the world that requires its citizens and permanent residents to file taxes even when they live abroad. Eritrea is the only other country to have a similar policy. This unusual policy a relic of the Civil War and the Revenue Act of 1862, which called for the taxing of U.S. citizens abroad — in part to punish men who fled the country to avoid joining the Union army.

This is no new policy — Americans abroad have always been covered by federal tax laws. However, things changed in 2010, when the Foreign Account Tax Compliance Act (FATCA) was enacted. This law essentially requires foreign financial institutions to check whether an account holder is a U.S. citizen or permanent resident. In some cases, Dunn said, they would ask for proof that the account holder is not a U.S. citizen.

The end result here is that whereas in the past a U.S. citizen abroad might be able to get away with not filing their U.S. taxes, that has become vastly less likely under these new circumstances. In some cases, this can be extremely costly: Johnson was known to have racked up a large U.S. tax bill for the sale of his home in London, even though he had not lived in the U.S. since he was a small child.

But even for those without Johnson's wealth, it can be tricky. “FATCA is a dirty word to Americans abroad,” Peter Spiro, a Temple University law professor and the author of “At Home in Two Countries: The Past and Future of Dual Citizenship,” explained. “Think lots of extra forms that have to be filed even by citizens who aren't wealthy by any standard. Americans abroad used to be able to do their taxes just like Americans at home. Now they have to hire expensive accountants.”

Giving up your citizenship isn't necessarily cheap either. It can take a long time to get an appointment in some places, and the processing fee is around $2,350. More important, Dunn said, was the “exit tax” that some high-earning or high-net-worth individuals have to pay — and also some people who forget to file their forms correctly too. But evidently, for some people it's worth it. (Green-card holders have a simpler and cheaper process.)

This isn't necessarily a huge problem, of course. The number of people who choose to become U.S. citizens each year is far over the number who renounce their citizenship or green card (there were 729,995 naturalized citizens in fiscal  2015, according to U.S. Citizenship and Immigration Services).

But it does send an unfortunate message. “It is a kind of no-confidence vote,” Spiro said. “If the numbers keep spiking, it will be best evidence that U.S. citizenship isn't the sacred thing it once was.” Some Americans abroad had hoped that the incoming Trump administration would be sympathetic to their arguments about FATCA, Spiro said, but it doesn't appear to be high on the agenda for the new White House.

In the end, Spiro wonders whether the Trump administration could ultimately add further to the growing wave of expatriation. “Many Americans who live permanently abroad have been proud Americans, and that's why they have kept their citizenship, the tax hassles notwithstanding,” he said. “But if you add repulsion to Trump in the mix, more may take the plunge and renounce.”

More on WorldViews

Boris Johnson, Britain’s foreign minister, has finally given up his U.S. citizenship

Can an American become a refugee? Yes, and some already have.

Almost 10,000 Syrians have registered to live in a country that might not exist