Why: After Confederate initiated and won the battle of Fort Sumter, the north was eager for the Union to make advancements. Union shot across the creek at the confederates to begin the battle.
"We are so going to win this battle, all we have to do is overtake the confederates, then overtake their government and capital."
What: This was the first MAJOR battle of the civil war. The Union planned on it being a quick battle, but instead lost due to their cockiness. Union troops marched from federal capital to strike Confederate force along Bull run (a small river).