currently signed up. nuclear powers agreed to reduce their arsenals in exchange. others agreed not to have them at all. and in the �*70s, the deals between the us and russia continued to more focused on long—range missiles. and though the rivalry of these superpowers intensified in 1991, there was the new start treaty. it aimed to decrease the size of their overall arsenals and underpinning the west. justification for these weapons is an idea called nuclear deterrence. the uk government factsheet states that potential aggressors know that the costs of attacking the uk or our nato allies could far outweigh any benefit they could hope to achieve. the possibility of mutually assured destruction being the strongest of reasons not to press the button. that's the theory, but it's under pressure. this week, the former russian president, dmitry medvedev, warned it may pull out of the new start deal, and both countries still have huge arsenals.