Sidney Tarrow

Political opportunities are changes in the wider political environment that make collective action more likely or potentially effective. In Power in Movement, Tarrow considers factors such as divisions among elites, access to institutions, and the state's capacity for repression.

A repertoire is the familiar set of protest methods available to people in a particular place and period. Demonstrations, petitions, strikes, occupations, and digital campaigns are not interchangeable tactics because each develops within a specific political history.

Tarrow describes cycles of contention in which successful early challenges encourage additional groups to mobilize. Authorities then adapt through reform, repression, or selective concessions, often causing the cycle to fragment or decline.

Tarrow collaborated with Doug McAdam and Charles Tilly on Dynamics of Contention. Their approach shifted attention from treating movements as fixed entities toward studying mechanisms such as brokerage, diffusion, boundary formation, and escalation.