There are two major differences between nuclear war and conventional war. Nuclear war could destroy the world in a matter of hours, while conventional war is waged gradually, with at least the possibility of reaching a settlement at some point before destruction has reached its maximum. Also, nuclear warfare potentially has long-term biological consequences which are far more severe than those of conventional warfare. Recent discoveries have even raised the possibility that these biological effects might cause the collapse of human civilization and, perhaps, the extinction of human beings.