McAdam, Tarrow and Tilly direct our attention to the level of the concrete social mechanisms that recur in many instances of social contention (Dynamics of Contention). They specifically refer to escalation, radicalization, brokerage, and repression as examples of social mechanisms that produce the same effects in the same circumstances, and that concatenate into historical processes and events. To this list I would add my own examples -- free-rider problems, norm diffusion, and communications networks.
I wholeheartedly endorse the idea that social explanations need to proceed on the basis of an analysis of underlying social mechanisms. But can this program be carried out in a Mendeleev sort of way -- try to discover a "table of elements" of causal mechanisms that aggregate into "molecules" of social contention?
The closer I look at the argument, the more concerned I become about the discreteness and elementality of the items MTT offer as examples. Take brokerage -- isn't this really an umbrella term that encompasses a number of different kinds of negotiation and alliance-formation? So brokerage isn't analogous to "expansion of ice during freezing" -- a clear example of a physical causal mechanism that is homogeneous across physical settings. Brokerage is rather a "family-resemblance" term that captures a number of different instances of collective behavior and agency.
If we find this line of thought somewhat persuasive, it suggests that we need to locate the causal connectedness among social settings at an even deeper micro-level. It is the situation of "agents with interests, identities, networks, allies, and repertoires" that constitutes the causal nexus of social causation on contention -- not a set of frozen mid-level groups of behaviors such as brokerage or radicalization. Instead, these mid-level concepts are descriptive terms that allow us to single out some broadly similar components of social contention.
Or in another vocabulary: the level at which we find real causal connections in the social world is the level of the socially situated and socially constituted individual in interaction with other individuals -- the perspective of methodological localism (Levels of the Social). This doesn't undermine causal realism -- but it does undermine the idea that there are meso-level "causal mechanisms" such as brokerage that really recur across instances.