6. In the course of the US Civil War, how did tactics change? O Massed groups of soldiers charged the enemy.
More of the responsibility was borne by the cavalry.
O Defensive trench warfare became more common.

On the Operational Strategic level (known at the time as Grand Tactics). The armies began to rely more and more on fortifying a position when they stopped movement. By the end of the war, soldiers, on their own initiative, began building primitive firing positions on their own.

Explanation:

:)

The correct answer to this question is this one: " d. the railways." As presented in the passage above, the central trend of is leading us to the construction of the railways and how the states are to be benefited to it. The states include New York (that had rail connections with) Chicago and St. Louis, Philadelphia and Pennsylvania, Ohio, Indiana, Illinois, Baltimore.