Meanwhile, Mao had ordered preparations for a "defense in depth" along the border because real fears had arisen of the border crisis escalating into all-out war. In a bid to repair China's image abroad, which had been badly damaged by the Cultural Revolution, Mao on 1 May 1969 invited diplomats from several Third World nations to attend the May Day celebrations in Beijing. To the assembled diplomats, Mao formally apologized for the attacks by the Red Guards against diplomats in China and the smashing up of the embassies in Beijing in 1967. Mao claimed not to be aware of the fact that the xenophobic Red Guard had been beating up and sometimes killing foreigners living in China during the Cultural Revolution. Also, Mao announced that for the first time since the Cultural Revolution he would send out ambassadors to represent China abroad (most Chinese ambassadors had been recalled and executed during the Cultural Revolution with no replacements being sent out). By then, Mao had felt that China's isolation caused by the Cultural Revolution had become a problem with China on the brink of a war with the Soviet Union.