Nationalism is back. From the rise of nationalist parties in Europe, to Brexit, to the election of an American President who declares “America First,” nationalism has once again become a buzzword in world politics. Despite its resurgence, however, our understanding of how nationalism shapes international outcomes and politics among nations remains incomplete. Ever since Stephen Van Evera lamented the lack of research on nationalism and war in 1994, there has been only moderate scholarly interest in nationalism in international relations. Jamie Gruffydd-Jones’s work therefore timely and welcome.