The bloodiest single day of battle in American history happened in the
A. Battle of Antietam
Explanation:
The Battle of Antietam took place near Shapsburg, Maryland in September 17 of 1862. This Battle was part of the battles fought in the American Civil War. The Union had 12,410 casualties with 2,108 dead. Confederate casualties were 10,316 with 1,546 dead.
As this Battle had a tremendous number of casualties in both sides and last only 1 day (it was over by 5:30 pm). it is considered the bloodiest single day of Battle in American History.
I believe a majority of major battles happened in these places because the British had control of them at some point. New York also served as the British base of operations so they probably wanted to break Britain's hold on these cities.