the 13th Amendment ended slavery in the United States. What would be the best reason Congress decided to amend the Constitution to make this practice illegal

One of the reason for the Congress to pass this law would be for a military strategy.

Explanation:

Back in those days, when the law was passed, America was under a civil war and to gain power in the south, where the states had most of the slaves in the country, the Preident proposed that law.

B >

Congress felt slavery was ethically and morally wrong.