The Kremlin crisis began when a bomb attack on the Kremlin, done by the Stalin's children terrorist group, Occurs on August 24th, 1961. The bomb killed several politburo members, and destroyed a significant portion of the building itself. Naturally, the USSR was suspicious of this, and immediately blamed NATO, and particularly West Germany.
Immediately after the Kremlin bombing, the Soviet army was ordered to mobilized. Although the army can't be mobilized in a day, the Soviets modified their Zhukov-4 plan, which is a plan for effectively mobilizing the Eastern European armies within two days. This deployment continues with The Soviet's nuclear arsenal turning to standby mode, rather than deactivated. the UK immediately requests the USSR to stop mobilization, threatening to attack if they continue. Belgium also begins to consider mobilization as well.
Escalation of the conflict
With the USSR mobilizing as fast as possible, both France and Belgium begin to mobilize. Thousands of troops are sent to the border between West Germany and East Germany, both sides struggling to counter the others deployments.