I would talk about the following things if I had to write an essayon this issue:
- It led to the issue of race as a major political issue in the United States. After the war, the issue of black rights becomes a big one and continues to be with us today.
- It led to the creation of the party system that we now have. The coming of the Civil War made the Republican Party viable and the war itself gave the party long-term credibility.
- It led to the current situation where the South is politically very different from the rest of the nation. This is going away a bit now, but the South is solidly conservative, and this conservatism is based to some degree on the legacy of the Civil War and the racial issues that followed.
- It clearly established the idea that the federal government is more powerful than the state governments. It made clear that the states could not override federal laws. Therefore, in a way, you can say that it made the US truly united for the first time in its history.