he calls "legal constitutionalism"". Schmitter places various scholars under each tradition: 1. Sociological constitutionalism: Some classic scholars in this tradition are: "Polybius, Machiavelli, Montesquieu, Benjamin Constant, Alexis de Tocqueville, Lorenz von Stein, Karl Marx, Moisei Ostrogorski, Max Weber, Emile Durkheim, Robert Michels, Gaetano Mosca, Vilfredo Pareto, and Herbert Tingsten." Schmitter argues that, in the twentieth century, this tradition was known by the label of "historical political sociology" and included scholars such as "Stein Rokkan, T.H. Marshall, Reinhard Bendix, Otto Kirchheimer, Seymour Martin Lipset, Juan Linz, Hans Daalder, Mattei Dogan, S.N. Eisenstadt, Harry Eckstein, and Dankwart Rustow." 2. Legal constitutionalism: Some classic scholars in this tradition are: "Léon Duguit, Georges Burdeau, James Bryce, A. Lawrence Lowell, and Woodrow Wilson." Schmitter argues that in the twentieth century this tradition was continued by: "Maurice Duverger, Herman Finer, Samuel Finer, Giovanni Sartori, Carl J. Friedrich, Samuel Beer, Jean Blondel, F.A. Hermens, and Klaus von Beyme." Periodization as a field of political science Gerardo L. Munck offers the following periodization for the evolution of modern comparative politics, as a field of political science - understood as an academic discipline - in the United States: 1. The Constitution of Political Science as a Discipline, 1880–1920 2. The Behavioral Revolution, 1921–66 3. The Post-Behavioral Period, 1967–88 4. The Second Scientific Revolution 1989–2005 Contemporary patterns, 2000-present Since the turn of the century, several trends in the field can be detected. End of the pretense of rational choice theory to hegemonize the field Lack of a unifying metatheory Greater attention to causal inference, and increased use of experimental methods. Continued use of observation methods, including qualitative methods. New concern with a "hegemony of methods" as theorizing is not given as much attention. Substantive areas of research By some definitions, comparative politics can be traced back to Greek philosophy, as Plato's Republic and Aristotle's The Politics. As a modern sub-discipline, comparative politics is constituted by research across a range of substantive areas, including the study of: Politics of democratic states Politics of authoritarian states Public goods provision and distributive politics Political violence Political identity, including ethnic and religious politics Democratization and regime change Elections and electoral and party systems Political economy of development Collective action Voting behavior Origins of the state Comparative political institutions Methodologies for comparative political research While many researchers, research regimes, and research institutions are identified according to the above categories or foci, it is not uncommon