This document discusses the concept of federalism, which refers to a system of government that divides power between a central national government and several state or local governments. It outlines some key aspects of federalism, including how power is balanced and shared between different levels of government. For example, the national government is responsible for issues like national defense, while states have powers over issues such as smoking laws. The document also examines different models of federalism and how the balance of power between national and state governments has evolved over time in the United States.