This lecture explores the evolving significance of environmental issues in international relations, emphasizing how they can lead to conflicts affecting global security. It covers pivotal concepts such as the Tragedy of the Commons, carrying capacity, and sustainable development. The lecture also delves into various driving forces of environmentalism, including core values, population growth, technology, consumptive behavior, and political economy. It concludes by highlighting seven major environmental challenges and their potential social impacts, along with their implications for future conflict.