Force refers to the use of physical, economic, or political power to achieve an objective. In the context of International Relations, force can refer to the use of military power, economic pressure, or diplomatic leverage by states or other actors to advance their interests or resolve conflicts. The use of force is a central concern in the study of International Relations, and the role and limitations of force in international politics have been widely debated by scholars and policymakers.
Source: Waltz, K. N. (1979). Theory of International Politics. Reading, MA: Addison-Wesley.