and it’s The First Battle of Manassas
It is known by both names.
The Union name was Bull Run; the Confederate name was Manassas.
The Union named its battles after natural features(Bull Run was a stream) while Confederates named theirs after towns or place names.
https://www.history.com/news/why-do-some-civil-war-battles-have-two-names
Well, yes, I agree with you there, but the other side got the privilege of naming things.