What was demonstrated by the first battle of bull run?

that the north would win
that the south was better trained than the north
that african american soldiers would be useful to the union
army
that the war would be long

The first Battle of Bull Run demonstrated that the war would be long and difficult. It showed that both the Union and Confederate armies were inexperienced and not fully prepared for the realities of war. It also showed that the southern troops were well-trained and organized, leading to a Confederate victory. Additionally, the battle highlighted the need for more African American soldiers to join the Union army to help tilt the balance of power in their favor.