The rise and expansion of the Mongol empire in the first half of the thirteenth century created a serious crisis in the tributary (冊封-朝貢) system, which had been providing a feasible framework for five hundred years for exchange between the mainland regimes like the Tang, Song, Khitan Liao and Jurchen Jin, and those on the Korean Peninsula including the Silla and Koryǒ, which allowed the latter de facto independence while ritually recognizing the suzerainty of the former. Despite the Koryǒ’s efforts for continuing the tributary system, the Mongols, imposing its own policies on the newly subjected countries,kept requiring the Koryǒ to fulfill a set of demands, or the “Six Obiligations”

中文翻译：

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歧义下的过渡：1260年前后的高丽-蒙古关系

十三世纪上半叶蒙古帝国的崛起和扩张造成了封朝贡制度的严重危机，这为唐等大陆政权之间的交流提供了五百年的可行框架、宋、辽契丹、金女真，以及包括新罗、高丽在内的朝鲜半岛的那些，允许后者事实上的独立，同时在仪式上承认前者的宗主权。尽管高丽人努力延续朝贡制度，但蒙古人将自己的政策强加于新臣服的国家，不断要求高丽人满足一套要求，即“六项义务”