Why did the federal government fight against the southern armies in the civil war?

The federal government fought against the Southern armies during the Civil War primarily to preserve the Union and maintain national unity. The Southern states seceded in response to conflicts over slavery and states' rights, threatening the integrity of the nation. The government aimed to uphold federal authority and prevent the expansion of slavery into new territories, which was seen as crucial for the future of the Republic. Ultimately, the war was also driven by a commitment to the principles of democracy and equality.