Shortly before Boris Johnson officially became Prime Minister of the United Kingdom on Wednesday, his counterpart in the U.S. drew a thread across the Atlantic. “They call him Britain Trump,” said President Donald Trump.

Trump was not the only one to notice some similarities between the two world leaders, like their penchant for outrageous remarks and checkered personal lives. But their nearly simultaneous accession to power has broader historical significance, as well. For more than two centuries, even when the nations have been in conflict, U.S. and U.K. politics have evolved in sync. At a series of turning points—in the 1860s, the 1900s, the 1940s, the 1980s and the 1990s—both governments have taken a new course, usually in the direction of greater democracy and economic equality, but more recently towards deregulation, fewer workers’ rights and public services, and inequality.

Trump and Johnson represent the latest step in that evolution—and it’s one the world would do well to heed.

Even in the era of the American Revolution, politics in the colonies and in Britain had more in common than might be expected of two opposing sides. King George III’s attempts to strengthen the monarchy at Parliament’s expense provoked loud opposition in Britain as well as in the colonies, and several leading British political figures openly sympathized with the colonies’ grievances. But the outcome of the revolution, and the subsequent French Revolution, put an end to any hopes that Britain would move in a more democratic direction any time soon. Not until 1832 did the British Parliament pass a law that made the election of the House of Commons a bit more democratic, while still leaving most adult males without the vote.

The American Civil War changed all that. The British public saw the war as a contest between northern democracy and southern aristocracy, and Lincoln became a hero to the British working and middle classes. Only two years after the northern victory, in 1867, a new Reform Act granted the franchise to most adult males in Britain, and further steps towards true democracy followed in the next two decades.

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In 2016, Donald Trump ran against three of the bipartisan establishment’s most cherished positions—greater immigration, free trade and U.S. leadership of a multilateral world order—and defeated establishment Republican candidates and his Democratic opposition. That same year, 2016, in Britain, Prime Minister David Cameron turned the issue of remaining in the E.U. over to the British people, and lost his gamble. Cameron’s successor Theresa May and the Labour opposition were then left to implement a move which they had opposed, and could not agree on how to do so.

Unlike Trump, Johnson was already a major if controversial figure within the Tory Party, and served as May’s foreign secretary. But he became Prime Minister largely because he had publicly supported Brexit. He was chosen to be the new P.M. by 92,153 members of the Tory Party at large, not its Parliamentary members—a change that dates from 1998, and which, like primaries in the U.S., makes it possible for an anti-establishment candidate to defeat its party’s traditional leaders.

Both Trump and Johnson have come to power because their electorates have repudiated longstanding policies and leaders from their nation’s political establishments. Now Johnson hopes to cut Britain loose from the E.U., a step that some predict may break up the United Kingdom within another decade. But that won’t be all he has to do. As President, Trump has started trade wars, repudiated international agreements like the Paris Climate Accord and the Iran deal, and declared war on immigration. We don’t know how far their disruption of the established order will go, but once again, the two greatest democracies of the Atlantic world have almost simultaneously embarked on parallel new courses.