The Founders gave us our Constitution on Sept 17, 1787, and I think one can argue that the Constitution was saved with the Battle of Antietam which took place exactly 75 years later. Although many look at that battle as a draw, I consider that it was a resounding victory for the North. First of all, Lee's much smaller army was bled white in that battle, and it would take a while to recover. Secondly, a main aim of the South, get the slave state Maryland to join the Confederacy, failed and all hopes of winning Maryland over to their side died with Lee's retreat back to the South. And thirdly, Lincoln considered it enough of a victory to issue the Emancipation Proclamation from a position of strength and with its issuance, any hope the South had in a European power coming to their aid vanished.