I seek to understand how political coalitions and communities of thought develop over time, as well as how ideas, especially ideas about foreign affairs and progressive reform, have intersected with people's lives and animated their actions. In my book, Promise and Peril: America at the Dawn of a Global Age (Harvard University Press, 2011), I explain the origins of modern American isolationism and track its development in relation to—and in tension with—new visions of internationalism and domestic reform from the 1890s through the 1940s. Under my Penn Mellon Fellowship, I am working on two new studies. The first is a transnational analysis of anti-imperialism, which situates William James's political philosophy within the wider narrative of transatlantic and worldwide anti-imperialist politics from the late nineteenth through the early twentieth centuries. My second project is a study of early Cold War conservative politics and the changing role of nationalist non-interventionism and isolationist arguments in U.S. political thought and party politics. I also serve as a senior editor for the new Oxford Encyclopedia of American Diplomatic and Military History, to be published in 2012.