What is "horizontal federalism"?

Horizontal federalism refers to the relationships and interactions among states within the federal system. This concept reflects how states cooperate, negotiate, and share resources or legislation with one another. For instance, horizontal federalism can manifest in various ways, such as through interstate compacts where states agree to work together on mutual interests, or through the Full Faith and Credit Clause, which requires states to respect the public acts, records, and judicial proceedings of other states.

Understanding this concept is essential because it highlights the collaborative nature of state governance and the importance of inter-state relationships in a federal system. While the other options touch on significant aspects of governance—such as the distribution of power within a single state, the federal framework's requirements, or the dynamics between local and federal authorities—they do not define the essence of horizontal federalism, which specifically pertains to the interactions among the states themselves.