Meanwhile, in Phnom Penh, the Kampuchean leadership had developed a fear and hatred of the Vietnamese leadership as a result of Vietnam's historical dominance over their country. From the Kampuchean perspective, the Vietnamese strategy to dominate Indochina involved infiltrating the communist parties of Kampuchea and Laos with Vietnamese-trained cadres. For that reason, when the first group of North Vietnamese-trained Khmer Rouge personnel returned to the country, they were immediately purged from the KCP. During the months following the defeat of the Lon Nol government, Pol Pot continued to purge the KCP and the Government of Democratic Kampuchea of those who he believed to be Soviet and Vietnamese agents. Then, in the context of the triumphalism that prevailed among the Khmer Rouge leadership—they claimed they had single-handedly defeated the "American imperialists"—Democratic Kampuchea began preparing for war against Vietnam.