Because the Union (the North) was the place where the slaves were free while the Confederates (the South) held the slaves to do their work.
White Southerners defended the institution of slavery on a several fronts. They stated that it was necessary especially for the economy, They argued that slaves were the only ones who could do the needed work to grow tobacco (and later cotton). The Southerners also argued that there was no reason to cinsider that slavery was immoral. They appealed to three sources to support this claim. First, they looked to Biblical times. They pointed out that there was slavery in the Old Testament and the New Testament and that Jesus never spoke against the practice. Second, they looked at classical antiquity. They claimed that the Greeks and the Romans counted on slaves Finally, they looked to the time of the Founding Fathers. They stated that the people who wrote the Constitution also had slaves.
The Han, Roman and Gupta empires all fell do to invasion. A strong, loyal army is necessary to protect the empire from invasion. All of these empires were first weakened by a succession weak governments. The trust and faith in the government was eroded over time. Internal strife by the people because of declining abilities of the government to govern weaken the state. The government should try to prevent internal rebellions by maintaining good governance over the people.
