Briefly explain one factor that would support the analysis by historians who believe that the closest the united states and the soviet union came to a full-scale war was during the cuban missile crisis

There missiles ready and pointed at each country by the enemy state. 

The movement of USSR missiles to Cuba caused an immediate reaction by the US. Negotiations worked back and forth to prevent a missile attack by either side. The US had missiles in Turkey which the USSR believed to be a threat to their safety. 

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