The concept of nuclear deterrence holds that the threat of nuclear war is sufficient to prevent an assault. This argument can be applied to other types of warfare as well. For example, if the threat of chemical or biological weapons was used as a deterrent then they would be called non-lethal weapons or NLWs for short. Nuclear deterrence means that we have reached the point where only one leader on Earth has the power to destroy all life on it. The leaders of Russia and America have the ability to destroy each other's countries with their nuclear arsenals, but they are not going to do so because both of them know that this would mean the end of humanity. Non-nuclear alternatives could include conventional forces (i.e., troops with guns and tanks) or strategic alliances. However, these options are not perfect because you can't be sure that either will come through for you. For example, Russia and America have signed a treaty on conventional forces not being used in Europe, but this doesn't mean they won't break it. Alliances can be broken by one party if they feel like it can't be done effectively without both parties working together.