Maxim Litvinov who often attended the sessions of the League and discussed with him the possibility of Soviet aid to China. In 1936, France and China upgraded their relations from the legation to embassy level, and Koo thus became the first Chinese ambassador to France. Fluent in French, Koo and his wife tried very hard to join the high society of Paris, believing it was the best way to make China's case to the French elite. At one party, a French society hostess who believed him to the Japanese ambassador told him: "Japan is a big power, becoming more powerful by the day. You will surely be able to shallow up China". Koo was forced to tell her that he was actually the Chinese ambassador and the last thing he wanted to see was his country being "shallowed up" by Japan. Likewise, Madame Koo tried to leave a party by asking her hosts to call for her chauffeur and her limousine, only for the Japanese ambassador's limousine and chauffeur to appear, as her hosts did not know the difference between Japanese and Chinese. Koo's two teenage sons embarrassed him by throwing deck chairs in a lake in a Paris park, and tried to claim diplomatic immunity when a French gendarme ordered them to stop. The incident attracted much adverse comment in the French newspapers about the badly behaving sons of the Chinese ambassador who were trying to abuse diplomatic immunity. The Chinese diplomats in Europe together with their families formed a closely knit group who frequently met to discuss matters of common concern. Koo together with Quo Tai-chi (the ambassador in London), Tsiang Tingfu (the ambassador in Moscow), Tsien T'ai (the minister-plenipotentiary in Brussels) and Liang Long (the minister-plenipotentiary in Prague) formed an informal group of intellectuals-turned-diplomats who had similar values and beliefs. The Chinese diplomats stationed in Europe were all intellectuals who given up promising careers in academia to pursue careers in diplomacy in order to best serve China. Cheng Tien-fong, the ambassador in Berlin, was considered to be the "weakest link" amongst the Chinese diplomats with the feeling being that he was unqualified to be a diplomat. The Sino-Japanese war In July 1937, Japan invaded China. On 7 July 1937, the Marco Polo Bridge Incident occurred, and the Japanese promptly sent 5 divisions into northern China that advanced on Beijing. Koo spent many sleepless nights in the summer