When and how did China lose its territory of Mongolia?

Mongolia was never part of China. The last time, 800 years ago, Chinese Song Dynasty was under Mongolian rule for over a century until Ming emerged and pushed Mongols back. read more

Recent history (early 20th century): both Mongolia and China was under Manchurian Qing Dynasty rule since 17/18th century, but Mongolia was autonomous to Manchuria. When Manchurian Qing started abiding the agreement between Mongol and Manchuria, Mongols declared its independence. read more

China needs more territory. They have big land but their population is much too. And also increasing, so they need more land. Of course Mongolia borders with China, so it could be potential victim /Borders with Russia too, but I don’t think they wouldn’t dare to argue with Russia, or won’t want/ Mongolia also rich by natural resources. read more

Only in 2002 did China stop considering Mongolia as part of their mainland area and removed it from maps of their territory! Ties with Russia remained strong, however, the Soviet Union forcefully established a communist regime in Mongolia — utilizing nefarious methods such as execution and terror. read more