45, titled "The Alleged Danger From the Powers of the Union to the State Governments Considered", is the 45th out of 85 essays of the Federalist Papers series.

45 was written by James Madison, but was first published by The New York Packet under the pseudonym Publius, on January 26, 1788.

The main focus of the essay is how the state and federal governments will function within the Union, while keeping the people's happiness in mind.

He wrote: "the States will retain, under the proposed Constitution, a very extensive portion of active sovereignty".

The state governments, Madison argues, are closer to the people and can focus on the welfare of the people, regulating ordinary affairs such as the lives, liberties, and properties of the people, as well as the internal order of each state, and should have numerous undefined powers to do so, while the national government, being bigger and possessing national resources, can bring victory in war, protect the people's liberty, and maintain peace between the states, and should have clear, few, defined powers to do so, mostly focusing on external objects such as war, peace, negotiation, and foreign commerce and national taxation.