What if the 54th Massachusetts had caputured Fort Wagner in July 1863? What effects would it have on the civil war? Would Charleston fall sooner, or would the Confederacy still hold onto it till the end? What about the effects of a black regiment facing certain death, captured fort Wagner? What would the reaction in the north be? Would shorten the war capturing Charleston?
Fort Wagner fell by siege some one to three months later. Glorious charges into the face of concentrated artillery and rifled muskets almost always ended in disastrous failure. The military technology in the American Civil War was wholly defensive. Not as bad as WWI before the introduction of fully machinegun proof tanks in 1918, but bad enough.
With few exceptions, such ACW attacks simply did not work. Two sides would bash away at each other until the more battered side withdrew.
If it had somehow been a success (say, the Confederates were in the midst of re-inforcing the garrison while wounded were being removed), there is the possibility that the Confederates (and Copperhead Northern Democrats) might well have tried to claim that the supporting White brigades carried the day (they did also suffer very heavy casualties), not the 54th Massachusetts. Since both Colonel Shaw and the commander of the assault (Brigadier General Strong) were killed, it would have been left to Major General Quincy Gilmore to "spin" the story however he may have wished to do so. I think though that with a victory to his credit, he might well trumpet the victory all the more.
Unfortunately, the to-the-knife nature of conflict between Union Blacks and Confederate Whites (often fought under the black flag) meant that it was not unusual for the Confederates in a battlefield to throw their reserves at a flank that was relatively unthreatened, but was facing Black troops. The idea being to effect a great slaughter of Black troops, and the hell with what happened elsewhere on the battlefield. IIRC this resulted in absolute disaster for the Confederates at Nashville. Better to lose a battle, and an army, and a city, and a state, to White Yankees, rather than lose a minor skirmish to a bunch of armed damned N-----s!
The only real strategic triumph I can recall that was enjoyed by Black troops in the Civil War was the all-Black XXIV & XXV Corps taking Richmond!

