The United States had to face several challenges in redefining the union after the war. Two main problems were: how to deal with the Southern states that were still angry for losing, and what they should do with the ex-slaves. It was difficult to get American together after many people died in the Civil war and big part of the South was destroyed by the battles.
Apart from that, they had other challenges such as: building a solid economy, creating a stable political system, preserving the national independence (reducing conflicts with other nations and the nation itself), fostering American shipping, consolidating public support, reducing debts, etc.
