This chapter examines significant events of the 19th and 20th centuries that shaped foreign policy, with a significant focus on the Cold War, detente, and the post–Cold War era. Understanding this background and historical context of foreign policy and international affairs is critical to appreciating the complexity of contemporary relationships and issues. The chapter discusses how foreign policy is crafted, and it examines the role, powers, tools, and limitations of each branch of government—executive, legislative, and judicial—and it reviews the procedural policymaking process. It also discusses the role of global governance and theories of international relations and explores the role of increased globalization. A state's foreign policy is largely shaped by its executive leadership, which can determine whether a state is globally engaged or detached—whether a leader is an isolationist or internationalist is consequential for the state and can impact the international order and balance of power.