Previous reports suggested something of a U.S.-China tug-of-war over Park’s attendance. South Korean media said that the United States was pressuring her not to go (reports later denied by South Korea officials). Washington was reportedly concerned about the optics of Park’s presence at the events, which will also be attended by Russian President Vladimir Putin.

The United States also wants to see improved ties between its allies South Korea and Japan, and China’s World War II celebrations are expected to continue Beijing’s year-long emphasis on Japan’s “wrong attitude” toward history. Both China and South Korea recently expressed dissatisfaction with Japanese Prime Minister Shinzo Abe’s statement on the 70th anniversary of Japan’s surrender.
China, meanwhile, was eager to have Park attend. Her attendance will be seen as a diplomatic “win” for China (particularly given the perception that the United States opposed it).

Available: http://thediplomat.com/2015/08/confirmed-south-koreas-president-will-attend-chinas-ww2-anniversary-celebrations/