The Union decisively wins First Bull Run in 1861

[The Mikado]

The first major battle of the Civil War at Manassas was a huge Confederate victory, leaving the Union Army running home with their tail between their legs, dashing Union hopes of an early win to the war. Does a Union win that July day at Manassas lead to Rebel morale breaking and an easy Union sacking of Richmond? After all, it was only two months into the war and the Confederacy itself was only a few months old, with a hastily assembled army full of officers who had been US Army officers mere months or even weeks before.

If this DOES break the back of organized Confederate military resistance, does the fact that the war ends swiftly lead to a reunited US with slavery at least temporarily preserved? With the South readmitted with, likely, no time spent as occupied territories and no Emancipation Proclamation, the Southern States could block a 13th Amendment. At most, the leaders of the rebellion (military and political) might be barred from holding office, which might get rid of the worst of the militant slave power ideologues like Davis and Stephens out of the government, but I certainly doubt without the vengeful desire to crush slave power as punishment for the war and treason we'd ever get the 14th and 15th Amendments out of that period even if slavery does eventually die.

[True Federalist (진정한 연방 주의자)]

Given the state of both armies that early in the war, even a decisive Union victory at Bull Run in 1861 would have left McDowell in no condition to pursue as the rebel Army of the Potomac skeddaddled off to Richmond. So in no way does it bring the end of the war in 1861. With so significant a change, it's doubtful Jackson gains his "Stonewall" sobriquet, and if he does, maybe General Bee can explain if he meant it as a compliment or insult.

So any Confederate collapse as a result of Bull Run would be political, not military, in nature. As of Bull Run, Tennessee had seceded but not yet formally joined the Confederacy. So it's possible that Bull Run leads Tennessee to attempt a Kentucky-like neutrality.

[President Punxsutawney Phil]

Given the state of both armies that early in the war, even a decisive Union victory at Bull Run in 1861 would have left McDowell in no condition to pursue as the rebel Army of the Potomac skeddaddled off to Richmond. So in no way does it bring the end of the war in 1861. With so significant a change, it's doubtful Jackson gains his "Stonewall" sobriquet, and if he does, maybe General Bee can explain if he meant it as a compliment or insult.

So any Confederate collapse as a result of Bull Run would be political, not military, in nature. As of Bull Run, Tennessee had seceded but not yet formally joined the Confederacy. So it's possible that Bull Run leads Tennessee to attempt a Kentucky-like neutrality.

Interesting.
How much sooner does the war end in this scenario?

[True Federalist (진정한 연방 주의자)]

Given the state of both armies that early in the war, even a decisive Union victory at Bull Run in 1861 would have left McDowell in no condition to pursue as the rebel Army of the Potomac skeddaddled off to Richmond. So in no way does it bring the end of the war in 1861. With so significant a change, it's doubtful Jackson gains his "Stonewall" sobriquet, and if he does, maybe General Bee can explain if he meant it as a compliment or insult.

So any Confederate collapse as a result of Bull Run would be political, not military, in nature. As of Bull Run, Tennessee had seceded but not yet formally joined the Confederacy. So it's possible that Bull Run leads Tennessee to attempt a Kentucky-like neutrality.

Interesting.
How much sooner does the war end in this scenario?

It might even last longer.  For all of McClellan's faults as a battlefield general, he was superb when it came to logistics and training, and he'd be unlikely to take command of the Union forces in the Virginia theater until at least 1862 if the Union wins Bull Run. Also, a neutral Tennessee would have all sorts of butterflies for how soon, or even if, Grant rises to prominence. But even assuming that other than Forrest beginning his military career in a Mississippi regiment, no significant changes in leadership happened, then it ends at most a year earlier in my opinion.

The Union winning Bull Run is unlikely to lead to permanent Union control of central Virginia, and even if it did, it won't make a significant change in relative military capability. An early loss of Richmond is what would make possible a significantly shorter war, not a change in Bull Run.

[The Mikado]

Given the state of both armies that early in the war, even a decisive Union victory at Bull Run in 1861 would have left McDowell in no condition to pursue as the rebel Army of the Potomac skeddaddled off to Richmond. So in no way does it bring the end of the war in 1861. With so significant a change, it's doubtful Jackson gains his "Stonewall" sobriquet, and if he does, maybe General Bee can explain if he meant it as a compliment or insult.

So any Confederate collapse as a result of Bull Run would be political, not military, in nature. As of Bull Run, Tennessee had seceded but not yet formally joined the Confederacy. So it's possible that Bull Run leads Tennessee to attempt a Kentucky-like neutrality.

My impression that one of Bull Run's biggest impacts was psychological, convincing the South that they actually had a real shot at this. The fledgling CSA losing the first battle of the war might convince the CSA that the secessionist cause was doomed way earlier than that sank in in our timeline.

[Unconditional Surrender Truman]

Given the state of both armies that early in the war, even a decisive Union victory at Bull Run in 1861 would have left McDowell in no condition to pursue as the rebel Army of the Potomac skeddaddled off to Richmond. So in no way does it bring the end of the war in 1861. With so significant a change, it's doubtful Jackson gains his "Stonewall" sobriquet, and if he does, maybe General Bee can explain if he meant it as a compliment or insult.

So any Confederate collapse as a result of Bull Run would be political, not military, in nature. As of Bull Run, Tennessee had seceded but not yet formally joined the Confederacy. So it's possible that Bull Run leads Tennessee to attempt a Kentucky-like neutrality.

My impression that one of Bull Run's biggest impacts was psychological, convincing the South that they actually had a real shot at this. The fledgling CSA losing the first battle of the war might convince the CSA that the secessionist cause was doomed way earlier than that sank in in our timeline.

IOTL the effect of the Union defeat at Bull Run was to harden Northern resolve —why wouldn't the reverse have a similar effect in the Confederacy?