In the late 7th century, the kingdom of Silla unified the Three Kingdoms of Korea and entered a period known in historiography as "Later Silla" or "Unified Silla". Later Silla implemented a national policy of integrating Baekje and Goguryeo refugees called the "Unification of the Samhan", referring to the Three Kingdoms of Korea. However, the Baekje and Goguryeo refugees retained their respective collective consciousnesses and maintained a deep-seated resentment and hostility toward Silla. Later Silla was initially a period of peace, without a single foreign invasion for 200 years, and commerce, as it engaged in international trade from as distant as the Middle East and maintained maritime leadership in East Asia. Beginning in the late 8th century, Later Silla was undermined by instability because of political turbulence in the capital and class rigidity in the bone-rank system, leading to the weakening of the central government and the rise of the "hojok" (호족; 豪族) regional lords. The military officer Gyeon Hwon revived Baekje in 892 with the descendants of the Baekje refugees, and the Buddhist monk Gung Ye revived Goguryeo in 901 with the descendants of the Goguryeo refugees; these states are called "Later Baekje" and "Later Goguryeo" in historiography, and together with Later Silla form the "Later Three Kingdoms".