Why was the end of the civil war the bloodiest?

The Civil War was America's bloodiest conflict. ... Nearly as many men died in captivity during the Civil War as were killed in the whole of the Vietnam War. Hundreds of thousands died of disease. Roughly 2% of the population, an estimated 620,000 men, lost their lives in the line of duty. :)

Explanation:

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.