It was a turning point because both the US and the USSR realised that, if they carried on and if they used nuclear weapons, it would lead to MAD (mutually assured destruction). After the Cuban Missile crisis a hotline was set up between the American President and the Russian Premier, while the Limited Test Ban Treaty was finalised in August 1963- the US and USSR agreed to ban the testing of all nuclear weapons in sea, in the sean and above ground. Underground nuclear tests were still permitted.