What If

If the Confederacy had won the battle of Gettysburg, I think that President Lincoln would have started to try and make peace with the south. Up until the battle of Gettysburg, the Union hadn't been doing so well in the war. Most of the soldiers didn't even know why they were fighting, which just proves that maybe the Union wasn't all that ecstatic about "preserving the union." They were just fighting. After another loss, and on their on land,  the Union probably would have just left it alone and negotiated a peace treaty because it wasn't much of a big deal anyways. The Civil War would have ended right after Gettyburg if the Confederates had won.
However, I don't think that the Confederates would have gained the foreign support of Britain and France. The South supported slavery and since slavery is morally wrong and those countries have already abolished slavery,  Britain and France probably didn't want to get their hands dirty with the whole slavery issue.