The formation, maintenance, and dissolution of military alliances is the result of strategic interaction among nations. In this paper, I argue that states’ alliance behavior is not only affected by characteristics of countries and dyads, but also by the behavior of other dyads in the alliance network. I also maintain that patterns of cooperation in other international networks, such as those constituted by states’ shared memberships in intergovernmental organizations (IGOs), have influence on how alliances are formed. To estimate these within and cross-network extra-dyadic interdependencies, I use temporal exponential random graph models. This allows to avoid the assumption of independence of observations which underlies the vast majority of estimation techniques employed by international relations scholars and to directly model interdependence effects of triadic and higher order within and across networks. I test my argument using data on international alliances from 1950 to 1992. Results suggest that both within and cross-network extra-dyadic dependencies exercise powerful influence on states’ alliance choices indicating that strategic interaction does neither stop at the dyad nor at the network level of analysis.