Why would states that are self interested cooperate in international regimes‪?‬

International regimes represent an integral part of globalisation and according to Little, the number of regimes increases steadily. Moreover, regimes account for a great deal of everyday convenience, ranging from seemingly simple practices like sending a letter abroad to the most complex economic interactions. In fact, “there is now no area of international intercourse devoid of regimes, where states are not circumscribed, to some extend or other, by the existence of mutually accepted sets of rules.”
Undisputedly, the realist paradigm dominates any debate in International Relations. “Realism has dominated international relations theory at least since World War II.” It is therefore obvious to begin the search for an explanation for the growing number of international regimes and states’ willingness to participate in them within realism itself. Yet, how can realism, that regards states as sovereign units concerned primarily with their own security and survival in an anarchic international system, account for extensive cooperation in regimes?
In order to assess whether realism provides a suitable explanation for the obvious success of regimes, this essay shall compare the realist approach to the neo-liberal account of regimes. Although the existence of international regimes is acknowledged by neo-liberals and realists, the two groups have competing theories about the formation of those regimes.
Having looked at these two different approaches to explain the existence of regimes, this essay shall argue that the notion of ‘self-interest’ is, perhaps surprisingly, the very reason why states would want to participate in regimes and not at all an impediment, as the question suggests. However, the realist explanation of regimes does not stress the importance of states’ self-interest as a cause for regime formation. It is the neo-liberal regime theory that holds that self-interest is a motive for states to cooperate in regimes. Hence, this essay will conclude that the realist theory does not provide an accurate account for the creation of regimes and their durability.