Things have changed since the days of the Marshall Plan
I know I am repeating myself, but it is a point that bears repeating: we are experiencing a worldwide resurgence of nationalism and the nation state and are now effectively living in a post post-Cold War world. This development frightens me, because a similar spike in nationalism, which came amidst the explosion of the global economy in the period from the 1850s to the 1910s, led two horrific world wars. It wasn't until the 1990s that the level of global trade returned to 1913 levels.
Evidence of this shift is everywhere, from Putin's invasion of Ukraine on nationalist grounds to China's invocation of nationalism to Donald Trump's appeals to ethno-nationalism to new nationalist governments in Eastern Europe and Latin America. Tomorrow the people of the United Kingdom are voting on whether to stay in the European Union, and right now the vote looks very close. While there is a tiny pro-Brexit left, most of the push is motivated by nationalists drawing on fears of immigration and the effects of multiculturalism. (The EU can be criticized on many legitimate grounds, but it is nationalism first and foremost that is driving this.)
This is a remarkable turnaround of events. The 1991 Maastricht Treaty, which turned the European Community into the European Union, was hailed in the aftermath of the fall of the Berlin Wall as the sign of a new, peaceful Europe free from the specter of war. Of course, the wars in the Balkans raging already in 1991 proved such hopes were overstated, and were perhaps a more accurate harbinger of the future than Maastricht.
There is no doubt that the EU has failed immensely in the last quarter century. It failed to meaningfully intervene in the Yugoslav wars. It overextended the euro, putting countries like Greece onto the currency that had no business being there, harming the Eurozone economy and making it difficult for Greece to recover due to it not having any control over its own monetary policy. The EU's organization itself is maddeningly bureaucratic, often undemocratic, and almost impossible to understand. When I taught a class on postwar Europe I didn't even bother trying to explain it to my students because I actually wanted them to be interested in their education.
So yes, there are reasons to want to change the EU, and I think it is in dire need of rethinking. However, the response in Britain (specifically England) has been motivated by notions of national sovereignty, rather than any desire to improve the EU or any real interest in its goals. So for me it is not the backlash against the EU that unnerves me, it's the nature of that backlash. Nationalism was responsible for a tremendous amount of bloodshed in the 20th century, including murderous campaigns blamed on communism that were actually part of larger projects of nation building. (I am thinking here especially of Stalin's Russia and Mao's China. Putin and Xi are just new players in an old and continuing nationalist narrative.) Not all nationalism ends in the concentration camp and bloody battlefield, but it is usually accompanied by narrowed minds and marginalization of the "other."
The European project originated out of a need, after the cataclysm of 1914-1945, to use economic integration as a way ensure peaceful coexistence. In that respect, it has been a massive success, so successful that so many are forgetting the fragility of that success. After World War I, the architects of the post-Versailles world system thought it would be permanent and were confident in its success. By 1933, it was already practically extinct, torn apart by nationalist demagogues and worldwide economic decline. Does that sound familiar to anybody? We are entering a new phase in world history, time will tell just what that means.