From 1231, Goryeo was intermittently invaded by the Mongol Empire. During this time, Goryeo was controlled by a military regime led by the Choe family. In 1232 the government under the nominal king fled to Ganghwa Island, which Mongol horse riders were unable to land on, and resisted the Mongol invasion. Unfortunately because of its fragile foundation, Goryeo faced frequent rebellions. The 1258 rebellion resulted in the establishment of Ssangseong  and Dongnyeong Prefectures  by the Mongols. Unlike these rebels, the Sambyeolcho  were an organ of the military government. They were organized by the Choe family to maintain security. However, unlike the Choe private guards unit , the Sambyeolcho assumed public functions performed by police and combat forces, effectively replacing the Six Divisions of the military. In 1258, Choe Ui, the fourth of the Choe family, was overthrown by Kim Jun  using the Sambyeolcho. Kim Jun took a pro-Mongol policy and sent Crown Prince Wang Jeon to the Mongol Empire. At the same time, King Gojong and the crown prince approached the Mongols to restore power from Kim Jun. In 1268, however, Kim Jun was annihilated by the Sambyeolcho under the order of Im Yeon. The next year, Im Yeon's attempt to replace King Wonjong was reversed by the crown prince  with the help from the Mongol force. In 1270, Im Yeon's successor Im Yumu was killed by the pro-Mongol faction using the Sambyeolcho. It marked the end of the military regime.. How many Mongol prefectures were established due to the rebellion in 1258?