Liberal internationalism has been in crisis for a while now. Yet, until recently, its supporters have argued that its prospects are better than ever, as the successful spread of liberal principles, practices and institutions in the international sphere provides the necessary basis for reform. Alas, recent political developments do not support these expectations. In fact, the Brexit vote, the election of President Trump, and the rise of populism more generally challenge liberalism in the domestic sphere and aim to unravel its international achievements. But the idea that these movements are therefore liberalism’s nemeses does not quite follow. Providing a theoretical and historical analysis of liberalism, this article shows that the separation of domestic and international politics is constitutive of liberalism itself. The successful extension of liberal principles into the international sphere undermines this separation and thus liberalism itself. Ironically, therefore, the prospects of liberal internationalism are dependent on the reestablishment of a clear divide between domestic and international politics. And this, I argue, is precisely the goal of contemporary populist movements.