He continued Oda Nobunaga’s work of unifying the country that had been fragmented by the feuds between daimyo. Between 1582 and 1591, by a mixture of military strategy and skilful diplomacy he broke their power. Mistrustful of the power of Buddhist monks, for a time he encouraged Catholic missionaries but later savagely persecuted Christians in Nagasaki. He built castles, carried out land surveys, and disarmed peasants. His ambition was to conquer China, and when in 1592 Korea, a vassal state of China, refused passage to his troops, his army numbering 200,000 captured Seoul and advanced north until Ming armies forced him to retreat. The Koreans routed him at sea. A second campaign was abandoned when Hideyoshi died. He appointed Tokugawa Ieyasu a guardian of his son, Hideyori.