What would have been the incentive for either side to start a war that would end civilisation for all times? I do understand that a lot of well paid people had

What would have been the incentive for either side to start a war that would end civilisation for all times? I do understand that a lot of well paid people had us buy weapons we don’t need for decades; they did a good job in convincing our parents and their parents that evil is just about to make its move. Just spend less money and have a compulsory military service. Young men without any military ambition from the very society they are supposed to protect are just very eager not doing anything and not shooting anybody up - until shit really hits the fan in their home country and they have to.