The fall of the Mongol Empire caused a serious crisis in the Mongolian society. Historiographers call this period “the age of lesser monarchs”. In effects, after 1368, the leaders of Mongolia reigned short time, and they were in permanent crisis with nobility. The khan lost a big part of his power. Local lords began to get more independent in their affairs. The once single old Mongolian nation disintegrated. Oirats seceded and formed their own monarchy. Mongolia broke in eastern Mongolia and western Mongolia. The eastern part divided into inner and outer territories. Oirats were quite active and sometimes raided into Central Asia.
The Mongolian language also separated in several distinct dialects that later became real languages. Nevertheless, the period going from the 15th to the 17th century was marked by important scholars and poets. For example, prince Tsogt was not only a warrior, but also a poet and philosopher. Buddhism arrived in Mongolia in the 16th century. In 1572, the khan Altan converted to Buddhism, and rejected the old shamanist beliefs. Buddhism brought to Mongolia literature, philosophy, theology, and natural sciences.
The khan's supremacy was limited in the post-imperial period. 22 khans ruled Mongolia between 1370 and 1634. Oirad prince usurped the throne in 1450, breaking the tradition of Genghis' descendants. Five years later, the dynasty was restored. In 1470, the khan Batmonkh unified Mongolia; this lasted 40 years, but his death entailed a further division.
From the 15th to the 17th century, the Mongolian lords producted many legal documents. During the empire, the great law Yasa was enough to govern the society. But when a prince wanted to become independent, he wrote new laws. For example, the legal code of the khan Altan was effective in the region of Tumed. And “the Mongol-Oyrat law” and the “religious code” are among the most important of these local laws.
In 1575, Manchus arrived and attacked the Chinese Ming dynasty. Their leader Nurhach declared his kingdom Qing in 1616. The Manchu army invaded Mongolia and put pressure on the Mongolian lords.
In 1636, the council of the lords of inner Mongolia admitted their defeat and recognised the authority of the Manchu emperor. The last descendant of the Genghis' line, the khan Ligden, resisted to Manchus until his death in 1634. Thus ended a great dynasty. This situation worsened because some Mongolians joined the Manchu army to share their victories. In 1691, the princes of outer Mongolia decided to accept the Manchu domination, leaving Zungaria as the unique independent province of Mongolia.