During his long and distinguished career, Charles Tilly addressed the problem situation he inherited from his teacher Barrington Moore, the situation that emerged in the middle of his studies, and the problems that arose later in his life. Moore's core themes were revolutionary classes, revolutionary violence, and the outcomes of revolution. As the 1960s and the 1970s gave way to the 1980s and 1990s, Tilly faced a different world-historical situation. So-called national liberation moments—violent and radical, communist and anti-U.S.—did not always win. And when they did succeed, radical politics was not particularly appealing. Tilly's final challenge involved rational-choice theory's drive for hegemony in explaining all outcomes—political, economic, and social—of macrohistorical change. For example, could a systematic alternative to the major approach to contention and conflict—a bargaining theory of war—be developed? To address these changing problem situations, Tilly fashioned his own unique theories, methods, and domains of inquiry. A truly seminal thinker, he pioneered now standard social-scientific approaches to mechanisms, contentious politics, and state construction. To understand Charles Tilly is therefore to understand the last fifty years of historical and comparative social science.