Which battle was one of the Union's worst defeats? Battle of Gettysburg

Battle of Antietam

Battle of Bull Run

Battle of Fredericksburg

I think it is the Battle of Bull Run. The First Battle of Bull Run, also known as the Battle of First Manassas, was the first major battle of the American Civil War. The battle was fought on July 21, 1861, in Prince William County, Virginia, just north of the city of Manassas and about 30 miles west-southwest of Washington, D.C.

Hope this helps

the answer is the government.

the answer to number 5 is fort sumter