Is it true that until the Civil War we did not capitalize the U in United States?
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The first two lines of the Declaration of Independence are:
The first two lines Article I of the Articles of Confederation of 1781 are:
So united was initially not capitalized, but United States with capitalization was adopted when the Articles were ratified in 1781.
Perhaps you're confusing the Articles of Confederation (confederacy: "a league or compact between two or more persons, bodies of men, or states for mutual support or common action" [M-W Unabridged]) with the secession of the Confederated States of America, which precipitated the Civil War.
I'm just a New Zealander/Englander but after reading bits of it I think the capitalisation is all over the place - which indicates that possibly there were all forms of writing it at the time.
So it's possible that there were conventions all over the country and the world that where not the same.