How did National Security Council 68 shape US foreign policy from 1945-1960?

The report of National Security Council 68 (1950) had a huge impact on the foreign policy of the United States from 1945 to 1960. At the time, the US was under threat from the Soviet Union, during the Cold War. The report, from the US Department of State’s Policy Planning Staff, recommended that the best way for the US to counter the threat of the Soviet Union was to build up their own weapons, creating an arms race.

We can see that this impacted US foreign policy in that the United States did test and assemble weapons, both nuclear and otherwise, as well as prepare their military so that they were poised to defend themselves should the Soviet Union attack. Additionally, the US followed the suggestions in the report to avoid isolationism, as the US continued to be involved in trying to negotiate with the Soviet Union. Finally, they followed the suggestions to not attack the Soviet Union themselves, as they felt that this would not be effective and would only create more devastating attacks.

How did George Kennan's "Long Telegram" and National Security Council 68 shape US foreign policy from 1945 to 1960?

Kennan's "Long Telegram" was the earlier of these two documents and proved deeply influential in shaping United States perceptions and strategy during the Cold War. It should be noted that Kennan's argument was based on his reading into Russian political psychology. According to Kennan, USSR political assumptions had been shaped by a long-standing Russian self-perception of political insecurity, prompting the Soviet Union to work toward expanding its own zone of influence in response. This led Kennan to advocate a policy of containment. His reading of the Cold War proved critical in shaping the alliance networks and political interventions of the post-war era. If you look at the Marshall Plan, or the alliance networks created to contain communist expansion, you would see his influence at work. (I've provided a link to the Long Telegram, courtesy of the Truman Library.)

NSC 68 took a more militaristic approach that Kennan himself criticized. NSC 68 regarded the USSR as "fanatical" and with "intentions to impose its absolute authority on the rest of the world" (quoted from the US State department—see link), calling for a dramatic expansion in US military capacity, so as to better defend itself and its allies. According to the US State Department, the Truman Administration would follow these suggestions: between 1950 and 1953, the military spending as measured by its percentage of the GDP would rise 300 percent in those years.