Kennedy did succeed in conveying the bottom line to Khrushchev on the most sensitive issue before them, a proposed treaty between Moscow and East Berlin. He made it clear that any treaty interfering with U.S. access rights in West Berlin would be regarded as an act of war.[146] Shortly after Kennedy returned home, the U.S.S.R. announced its plan to sign a treaty with East Berlin, abrogating any third-party occupation rights in either sector of the city. Depressed and angry, Kennedy assumed that his only option was to prepare the country for nuclear war, which he personally thought had a one-in-five chance of occurring.[147]
In the weeks immediately following the Vienna summit, more than 20,000 people fled from East Berlin to the western sector, reacting to statements from the U.S.S.R. Kennedy began intensive meetings on the Berlin issue, where Dean Acheson took the lead in recommending a military buildup alongside NATO allies.[148] In a July 1961 speech, Kennedy announced his decision to add $3.25 billion (equivalent to $29.47 billion in 2021) to the defense budget, along with over 200,000 additional troops, stating that an attack on West Berlin would be taken as an attack on the U.S. 