Answers:
1a- First Battle of Bull Run: Confederates won, shattered the North's hopes of winning the war quickly. Seven Days' Battle: Union army was forced to retreat from near Richmond. Second Battle of Bull Run: Confederates won a major victory.
1b- I think the Union lost because there were several units of Confederate soldiers, and during the battle, more soldiers and volunteers kept coming. The Union army also found Lee's battle plan at an abandoned Confederate camp.
2a- They divided their army. The Union army also found Lee's battle plan at an abandoned Confederate camp.
2b- The Battle of Antietam ultimately affected the North and the South because 1) it was the bloodiest day in all of US history (both sides lost a lot of men) and 2)Lincoln was able to draft the Emancipation Proclamation.
3a- Naval blockade of the Confederacy (Anaconda plan) to hurt their economy.
3b- They had much better armor and moved faster. Since the confederacy won, it gave them hope they could win the war.