Perhaps the BEST B1G Forum anywhere, here at College Football Fan Site, CFB51!!!

https://www.livescience.com/42716-epic-battles-that-changed-history.html

One list.  I think I'd substitute a few into the list:

Fall of Constantinople
Relief of the Siege of Vienna
Caesar and Vercingitorix?
Edington

I don't think Napoleon's invasion of Russia would "count", and the one major battle fought was not really determinant.(Borodino)

I would think about Trenton as more significant than Yorktown.

Anyway, I'm pondering battles that COULD have gone the other way and the ramifications would have been climactic.

Antietam.  A Confederate victory likely would have secured British and French recognition and assistance.

Was there much chance of a Confederate victory though?  I suppose an alternative is if Lee's orders had not been found and McClellan moved even slower than he did.

I suppose then the site of the battle would change to somewhere else, maybe Gettysburg ...

My personal opinion is any Civil War battle shouldn't be on the lost.  Reason: even if the confederacy had won, in some strange reality, there would have been another war within 20 years to the same purpose and ends, and what resulted would have resulted if there would have been one, two, three or more wars.... it's fortunate there was only one and so we wouldn't have been so weakened as a nation another nation could easily take us out. 

Outside of that and using the same logic, it narrows the battles that truly impacted world history down to those that truly altered trajectories of empires. 

The Seven Days battles of course were tactically relatively indecisive.  Malvern Hill was a southern disaster of a sort.  I know McClellan was being fed a line about the South having 200,000 troops.  It was weird that Pope would try and come south while McClellan's forces were still en route.  Problem with wanting glory instead of results.

There are some battles in history like Cannae that were astonishing in a tactical sense but later led to a strategic defeat.  Invading Russia seems like a bad idea.

Imagine the Nazis had been able to take the Caucasus and just wall of Stalingrad as they did Leningrad and the oil dries up for the Soviets.

I don't know if they really could have done that longer term.

McClellan is a very odd duck to me.  Lincoln turned to him again after this mess and he could have ended the war at Antietam, most think, had he put all his troops into the attack instead of piecemealing it.  He had Lee up against a river with only part of his army assembled, admittedly in a solid defensive position.

Council of fears.

That would be a good name for a book, sort of Tom Clancy like.

The Seven Days battles illustrate something interesting, one commander defeating the other commander without defeating his troops.  Tactically, the Union won more than it lost in the Seven Days.  Strategically, McClellan (always ready and willing to believe that he was outnumbered 2 to 1 when the reverse was true) was beaten back even has his subordinates were giving better than they got.

What did Lincoln say? Something like "if I gave him a million men,he'd swear the enemy had 2,and he'd lay down kicking and screaming for 3"

CWS what did Stalin tell the Japanese about Anglo-American intentions? - you mentioned this

Oh,Old Abe tried everything and said both of those.McClellan was reincarnated in the form of Montgomery - do very little,deflect all blame and weasel in on the credit