Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I say who wrote them.
Russett and Oneal. 2001. Triangulating peace: Democracy, interdependence, and international organizations. New York: W. W. Norton.
There are three variables (X) which produce peace (Y). Each X also helps produce the other two. In addition, peace helps produce the three Xs. The three Xs are democracy, econonmic interdependence, and membership in IGOs. These are basically Kant's variables. All these variables strengthen one another in a "virtuous cycle."
These variables have both dyadic affects and systemic affects. Dyadic effects means that a dyad is more peaceful if it has democracy, economic interdependence, and IGO membership. Systemic effects means that the level of democracy, interdependence, and IGO membership in the system has an independent effect on each dyad, regardless of the individual states' democracy, interdependence, and IGO membership.
Thus, there is systemic evolution.
However, this evolution is the result of states making strategic choices. They can choose to reverse the virtuous cycles and engage in vicious cycles of warfare. Either one is an equilibrium.
CONSTRUCTIVISM AND RATIONALISM:
The authors base their argument on a hodgepodge of constructivist and rationalist mechanisms. Jacob's handout summarizes them nicely (there's lots of them). Here's a sampling:
Research on similar subjects