CHICAGO (Reuters) - China on Wednesday bought at least 500,000 tonnes of U.S. soybeans in its first major purchase of the oilseed since U.S. President Donald Trump and his Chinese counterpart Xi Jinping struck a trade war truce earlier this month, traders said.The sales are one of the clearest signs yet that a bitter trade fight between the world’s two largest economies is thawing following the meeting of the countries’ leaders at the Group of 20 industrialized nations gathering in Argentina.Chinese state-owned companies bought at least $180 million of soybeans, two U.S.