In the course of the us civil war, how did tactics change? . a. battles at sea were more decisive than those on land.. b. defensive trench warfare became more common.. c. massed groups of soldiers charged the enemy.. d. more of the responsibility was borne by the cavalry.

The US Civil War was, as the terms states, a civil was in the United states which started at 1861 and ended at 1865. It started due to the differences between the slave and the free states in terms of power of the government to not allow having slaves in places which were not declared states yet. 

Defensive trench warfare became more common was the tactic chnge during the civil war.