Short answers, pulled from the story.
The Richmond-Petersburg campaign was a nine-month series of battles around Petersburg, Virginia, fought from the 9th of June 1864, to the 25th of March 1865, during the American Civil War. Despite its popular name, it was not a classic siege but a campaign of trench warfare in which Union forces commanded by Lieutenant General Ulysses S. Grant assaulted Petersburg and then constructed trench lines extending over 30 miles.
Petersburg was the primary supply center and railroad junction for Richmond, the Confederate capital, connected by five railroads and sited on the Appomattox River. Capturing Petersburg would cut off Richmond's supply lines and make it impossible for Lee to continue defending the Confederate capital.
On the 30th of July 1864, Union forces detonated 8,000 pounds of gunpowder in a mine shaft beneath Confederate works at Elliott's Salient, creating a crater 170 feet long and 30 feet deep that instantly killed between 250 and 350 Confederate soldiers. The assault that followed was poorly led, with troops moving into the crater rather than around it, and Confederate forces under Mahone counterattacked and trapped them inside. Union casualties reached 3,798, and Grant called it "the saddest affair I have witnessed in the war."
Petersburg had the largest concentration of United States Colored Troops of the entire Civil War, organized by December 1864 into the XXV Corps numbering between 9,000 and 16,000 men. USCTs participated in six major engagements of the campaign and earned 15 of the 25 Medals of Honor awarded to Black soldiers in the entire Civil War.
The Confederacy used both enslaved and free Black men for labor throughout the campaign, including building the Dimmock defensive line in 1862. In January 1865, Robert E. Lee wrote to the Confederate Congress urging legislation to arm and enlist enslaved men in exchange for their freedom. Congress passed the legislation on the 13th of March 1865, but emancipation remained conditional on a master's written consent.
After the failed Confederate breakout attempt at Fort Stedman on the 25th of March 1865, Grant's forces broke through the Petersburg lines on April 2. Petersburg surrendered at dawn on April 3, and Richmond fell the same evening. Lee retreated west and surrendered at Appomattox Court House, effectively ending the Civil War.