How did the war affect the need of railroad

It depends on the war.

Explanation:

Based on the question, I'm going to assume you're asking about the Civil War.  Railroads were needed during the civil war to transport soldier, equipment, and supplies to both the North and the South.

i think the answer is c, rivers.

explanation:

sometimes, borders fall along natural boundaries like rivers or mountain ranges. for example, the boundary between france and spain follows the crest of the pyrenees mountains. for part of its length, the boundary between the united states and mexico follows a river called the rio grande. the borders of four countries divide africa’s lake chad: niger, chad, cameroon, and nigeria.

they united the colonies in their fight against the british.