Total war is total both in how it engages societies and expands the targets considered permissible to attack and in its aims. Instead of one side saying, ‘Look, we'll just try and get the other side to recognise they've been defeated, and then we'll have a negotiation’, total war becomes about obliterating the other side, totally destroying the other side, totally defeating the other side.
We see it even more in the Second World War when the technology made it possible to hit the enemy’s homelands in ways that weren't possible in the First World War. You have: the mass bombing of Germany by the British and American air forces, the bombing of Japan, Japan's bombing of Chinese and Filippino cities, Germany’s bombing of cities like Warsaw and Rotterdam and of course, London. The expansion of the targets was huge in the Second World War, and the potential for causing destruction was that much greater. It ended with two terrifying, monumental bombs, the atomic bombs – the first time and last time so far ever used – dropped on Hiroshima and Nagasaki, which leveled those cities and killed thousands of people.
There was also the aim, in the Second World War, of destroying the societies that they had defeated. You see it in the Nazis – how they tried to turn vast swaths of Europe’s population into slaves, essentially, working to feed the German war machine and German society. The Japanese did something similar. The allies, for their part, sought unconditional surrender. In other words, the enemy – in this case, Germany, Italy, Japan, and some of their allies – had to surrender completely and put themselves completely at the mercy of those who had won.