This chapter shows how the national patterns of strike activity have changed at different periods of political rule between 1945 and 1963, and how these changes reflect the evolution of workers’ organization and elite intransigence with respect to working-class protest. The period of repressive populism saw the dramatic decrease in strike activity. The large differences in average size of the strikes seem to have been more the result of growth of the working class and the increase in the size of establishments than of mobilization capacity, considering the high strike rates in both periods. Organized labor’s use of the mass strikes as its major means of exerting pressure in the national political arena was the consequence of the rapidly evolving political crisis of the populist regime and of the growing counterpressures from the military establishment and middle and upper class interest groups.