Question

Why was Fort Sumter's location important?

Answer 1

Fort Sumter controlled the access to the port of Charlestown South Carolina one of the most important ports in the South.

Explanation:

With the Union forces in control of Fort Sumter the north could prevent any shipping coming in and out of Charlestown. Charlestown was important in the export of cotton necessary for the economic survival of the South.

The South hoped that the north would recognize its "rightful" claim to be able to succeed from the Union and form an independent nation, a second American Revolution, a new democracy, free from the economic taxes, and exploitation of the northern states

To be successful as an independent nation the south needed free access to all of its ports, particularly New Orleans, and Charlestown.
The south asked, demanded and threatened the commander of Fort Sumter to peacefully surrender the fort to the forces of South Carolina. ( "its rightful owner" )

When the Union Commander refused to give up control of what he considered to be property of the Union of the United States, the South Carolina forces fired on the Fort forcing its surrender and starting the Civil War.