July 1863 is definitely too early to call it inevitable. Sure the Union was superior in men and materiel by this point, but there were still 2 full years of fighting left. And that’s not counting the Election of 1864, which was nowhere near a sure thing https://twitter.com/khornefed/status/1277705948757254144

Right up until August 1864, the Republicans and Lincoln himself doubted they could win the election. Grant’s campaign was extremely bloody and the Confederates invaded Maryland and threatened DC. The Republicans even considered dumping Lincoln for a different candidate

Of course, McClellan was running on a peace ticket, so a Democrat victory in November could’ve clinched Confederate independence

It really wasn’t till Sherman captured Atlanta and Phil Sheridan drive the Confederates out of Maryland that the election looked more certain

I think the only point we can start considering things set in stone is after Lincoln’s victory in November