"The power vacuum in Europe after World War II induced the United States and the Soviet Union to seek European allies against one another (an action that neorealists would describe as “external balancing”). The disparate geopolitical circumstances facing the two superpowers were bound to have some effect on the types of alliances they sought. In the United States, many officials and legislators initially were reluctant to maintain a permanent military presence in Europe. They planned instead to help the West European states themselves acquire the wherewithal to sustain a viable balance against the Soviet Union. Not until after the outbreak of the Korean War in June 1950 did U.S. perceptions of the Soviet threat change enough to generate widespread support for a huge increase in the U.S. military commitment to Western Europe. By that point, U.S. officials already sensed, from the Berlin crisis of 1948–1949, that the United States would need an extensive network of military bases in Western Europe if it wished to deter or rebuff Soviet probes on the continent. The increased deployment of U.S. troops and weapons in Europe from late 1950 on was geared toward that end, and was also intended to reassure the West Europeans of the strength of the U.S. commitment to their defense. That commitment had been nominally codified in April 1949 – primarily at the West Europeans’ initiative – with the establishment of the North Atlantic Treaty Organization (NATO), but it was not until the early 1950s, after the shock of Korea, that the United States began putting up the resources needed to fulfill its military obligations to NATO."(...)