Which power is NOT reserved to the states?

The power that is not reserved to the states is the authority to declare war. This power is explicitly granted to the federal government under the U.S. Constitution, specifically in Article I, Section 8, which enumerates the powers of Congress. The states do not have the authority to independently engage in such significant military actions, as this could lead to fragmentation of national defense and inconsistent foreign policies.

In contrast, establishing local governments, regulating intrastate commerce, and conducting elections are powers that fall under state authority. The Constitution allows states to create their own local governments to address regional needs, regulate commerce that occurs within their borders (intrastate), and manage the administration of elections, including those for state and local offices. These powers have been historically recognized as essential to maintaining state sovereignty and governance.