By Marco Polo bridge incident, Japan opened the full aggression against China, and the United States to Japan's diplomatic relation was not same, but changed with the US interests. After the incident, the US attitudes changed from positive to negative to vice-positive, from "denied" to obey to the "neutral" until sanctions against Japan. The changing reason is that interest is the first principle, the domestic long-term prevalence of pacifism, isolationism, and US-japan trade relationship more important. During this period, the policy to Japan, objectively speaking, was a failure of diplomacy, which both hit the Chinese anti-japan behavior, also encouraged Japan's invasion.