Short answers, pulled from the story.
Strategic bombing during World War II in Europe began on the 1st of September 1939, the same day Germany invaded Poland, when the Luftwaffe started bombing Polish cities and civilian populations. One of the first major acts of bombing was the attack on the town of Wieluń, which had little to no military value.
Aerial bombardment of civilian areas was not explicitly prohibited by positive or specific customary international humanitarian law at the time. The Hague Conventions of 1899 and 1907 addressed land and sea warfare but were adopted before the rise of air power, and repeated diplomatic attempts to update the laws to cover aerial warfare failed before World War II began. General Telford Taylor, Chief Counsel for War Crimes at the Nuremberg Trials, noted that Axis leaders who ordered civilian bombing were not prosecuted for it.
Estimates of the death toll from strategic bombing range from hundreds of thousands to over a million. Millions of civilians were made homeless and many major cities were destroyed, especially in Europe and Asia. The bombing of Hamburg alone in 1943 killed roughly 45,000 people.
On the 14th of February 1942, the area bombing directive was issued to RAF Bomber Command, authorizing forces to be used without restriction and focusing operations on the morale of the enemy civilian population, particularly industrial workers. The directive followed a paper by Professor Frederick Lindemann arguing that bombing German cities would dehouse the workforce and reduce their ability to work. Aiming points were to be built-up areas, not specific industrial facilities.
According to the United States Strategic Bombing Survey, only about 20 percent of bombs aimed at precision targets fell within a 1,000-foot radius of the aiming point overall. In the fall of 1944, only seven percent of all bombs dropped by the Eighth Air Force hit within 1,000 feet of their aim point. The American Eighth Air Force received its first H2X radar sets in December 1943 and within two weeks was authorized to area-bomb cities using radar guidance.
The record attack on a single target in World War II was the bombing of Dortmund on the 12th of March 1945. A force of 1,108 aircraft, including 748 Lancasters, 292 Halifaxes, and 68 de Havilland Mosquitos, dropped more than 4,800 tons of bombs, destroying 98 percent of buildings across the city centre and the south of the city.