By May 1969, the level of intensity of the conflict had reduced substantially. Isolated incidents continued to occur particularly along the ROKA-controlled sectors of the DMZ, but it had become clear that the North had abandoned its hopes of starting an insurgency in the South. Qualitative improvements in the ROK Army meant that the U.S. could start to contemplate reducing its military presence in South Korea. On 25 July 1969, President Nixon announced his Nixon Doctrine that, henceforth, the U.S. expected its allies to defend themselves with U.S. air and seapower support , but not U.S. ground troops. While aimed primarily at South Vietnam, this policy would also apply to South Korea . On 1 October 1969 General Bonesteel handed over command of USFK to General John H. Michaelis. One of General Michaelis' early tasks was negotiating the release of three U.S. soldiers captured when their OH-23 helicopter was shot down after straying across the DMZ; their release on 3 December 1969 is regarded as the official end of the conflict.
Question: What way did the Nixon Doctrine not expect the U.S. allies to defend themselves by?
Answer: not U.S. ground troops