The mississippi river was a key factor during the civil war because
a. it was an important source of drinking water.
b. it divided the south’s territory in half.
c. it was the only route inland for the union navy.
d. it was needed as a port for european troops.

B.It divided the South’s territory in half.

Explanation:

The Mississippi River was the essential course for the Confederacy when bringing goods, commerce, and transportation.  

With the "Anaconda Plan" General Scott proposed an arrangement to get a bar of southern ports and caught the Mississippi River cutting the south into two. By 1862 the endeavors to catch the Mississippi River began and as arranged the south was in the long run partitioned, being the Union powers the ones winning the American Civil War.