June 4 marks a century since the signing of the Treaty of Trianon, the forgotten cousin of the Treaty of Versailles, which ended World War I. The Versailles pact settled the war on the Western front; Trianon dealt with the thorny question of borders in Central Europe and the status of the Hungarian portion of Germany’s wartime ally, Austria-Hungary. 

The Treaty of Trianon is little remembered today in the United States, but it is an ongoing controversy among the nationalists of Central Europe. Trianon is remembered above all in Hungary, which as a result of the agreement was cut down in size and saw Hungarian-speakers ‘stranded’ abroad in neighbors, such as Romania, Slovakia, and Serbia. Even today, after waves of ethnic cleansing in the 20^th century, the borders of Central Europe do not perfectly match the ethnic map.

Hungarian strongman Viktor Orban has consolidated power in part by promising to defend the rights of Hungarians abroad. Just several weeks ago, he posted a map of Hungary’s pre-Trianon borders on his Facebook, prompting angry reactions from his neighbors. Like his predecessors who led post-Trianon Hungary, Orban is whipping up nationalist tension to gather support for dismantling democracy.

The Trianon order was first torn down in 1938, after the Munich Conference opened the door to Hungarian territorial demands on Czechoslovakia. As Hitler’s Germany rose in power, so, too, did Hungary, bent on recovering the territory that it had lost. As Nazi Germany sought ethnic purity, so, too, did Hungarians, sending Jews and other minorities to death camps.

What went wrong with the Trianon treaty? It wasn’t that the Trianon order lacked international lawyers or well-meaning multilateral organizations. After World War I, the states of Central Europe signed treaties promising to protect ethnic minorities. The League of Nations assisted in the financial reconstruction of Hungary after World War I as a sort of proto-International Monetary Fund. Hungary even signed the Kellogg-Briand Pact, promising to outlaw war. None of this mattered much at all when the fascists saw an opening to redraw the map. The borders established in Trianon were only as durable as the strength of those forces that wanted to defend them. After being torn down in the run-up to World War II, they were only reestablished with the force of allied arms.

It is fashionable today in Europe to pretend that the continent’s peace and unity is guaranteed by historical inevitability or that it is upheld by the European Union’s legal order. In the United States meanwhile, prominent voices on the left and right both question whether the U.S. need concern itself with “quarrels in faraway countries, between people of whom we know nothing,” as British Prime Minister Neville Chamberlain famously described Czechoslovakia in 1938, as the Nazis dismembered it.

Comparisons between our present day and the 1930s have been commonplace in recent years. They are usually misleading. But in some places, the wounds of the interwar period feel fresh, while politicians seek benefit by reopening them. Hungary’s government has repeatedly attacked George Soros, its most famous citizen, using anti-Semitic tropes. It has chased the best and most independent university in Central Europe out of Hungary. It has seized extraordinary power to rule by decree.

Can anyone stop this authoritarian turn at geographic center of Europe? The European Union, despite its aspirations to geopolitical influence, has struggled even to issue press releases, being about as effective in defending democracy or confronting anti-Semitism as was the Kellogg-Briand Pact in outlawing war. The United States has plenty of its own problems at home and wants Europe to manage its own affairs.

But the ghost of Trianon is still haunting the continent. In the 1990s, the region’s competing nationalisms were stashed in the closet under Western pressure. Now, as America looks away and the European Union looks on impotently, they risk reemerging. Orban is marking the centenary of Trianon, meanwhile, by constructing a grand new monument outside Hungary’s parliament, mournfully listing all the territory beyond its borders that Hungary has lost, but has not forgotten.

The views expressed in this article are those of the author alone and do not necessarily reflect the position of the Foreign Policy Research Institute, a non-partisan organization that seeks to publish well-argued, policy-oriented articles on American foreign policy and national security priorities.