This week (April 3) in 1865, the city of Richmond fell to Union forces, which marked the beginning of the end of the Confederacy. Richmond had been not only the capital, but also the military headquarters, transportation hub, industrial heart, prison, and hospital center of the Confederacy. For 10 months prior, General Robert E. Lee had been able to keep Union forces at bay while defending Petersburg, but his depleted troops and scant supplies forced the General to make some hard decisions.
The citizens of Richmond had become accustomed to the sound of artillery from the South, and had lived under the threat of a Northern invasion of the city for a long time. But their faith in Robert E. Lee was firm and they never believed he'd allow the city to be captured.
Lee, however, had always felt constrained by his need to defend the capital city, and in letting it fall, he believed he be freer to make better choices for the entire Confederacy.
So as Confederate forces ultimately retreated across the James River and south of the city, they set fire to storehouses of tobacco and supplies on the riverfront. Strong winds stoked the fires, and unruly residents and soldiers helped spread the destruction. Turns out, city officials had read about the destruction of Columbia, SC (when Union soldiers had arrived, found stores of whiskey and went on a rampage, leaving the city in shambles) and hoped to avoid a similar result by ordering that all whiskey be destroyed. Because they were in a hurry, the stocks of every saloon and warehouse were smashed and poured into the gutters and down street drains. The smell attracted hundreds who gulped the whisky from off the street or scooped up in their boots and hats, and then set about destroying the city themselves (incited in part by scallawags who'd been hoarding food and clothes and had brought them out to try and make a profit - which infuriated an already stressed crowd).
All or part of at least 54 blocks were destroyed.
When Union troops entered the capital of the Confederacy, their first task was to battle the flames and save the city from complete ruin. Note: the Civil War was effectively over six days later when Lee surrendered at Appomattox.