You may be looking for the Union.

Federal Union or just Union was a legal term of art meaning the government of the United States of America, as created by the union of the states under the United States Constitution. It had particular meaning during the American Civil War, wherein "Union" was a common name for the United States Army, and where the "Federal Union" was the legal entity from which the Confederate States of America had seceded. Proof of this was found simply in the titles of many documents, most notably the Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union. (PROSE: Blood and Hope)

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