Answer: An extended siege.
Step-by-step explanation:
General Ulysses S. Grant had first tried to take Vicksburg in 1862 but failed and had to try again because Vicksburg was a very important town that sat on the Mississippi river and would give the Union control of the river if it fell.
After Grant defeated General John C. Pemberton close to Vicksburg, Pemberton retreated to Vicksburg where he was trapped by Grant who fended off attacks to liberate the city and constantly bombarded it from Union positions.
Ordering his soldiers to build 15 miles of trenches around Vicksburg, Grant was able to starve the city for 47 days such that Pemberton was forced to surrender to the Union.