I have been recently told by acquaintances that not only was the history of Mulan inspired by real facts, but that most of the military leaders of the Chinese Three Kingdoms and Japanese Sengoku periods were not the burly, hairy men that appear in official history, but actually fairly young and dainty females!
At first, I took it as revisionist nonsense -- these were, after all, the same people that tried to convince me that King Arthur had actually been a charming blonde -- but after a few searches, I found several educational games in which the player has the opportunity to simulate long conversations with these leaders between some of their most famous battles, and even become their most intimate confidant. Sadly, due to language barriers, I haven't been able to actually play any of these, so for now I can only sate my curiosity by asking you what forces led to this curious state of affairs. While the presence of female combatants in early militias was relatively common, one usually only became a military commander in extraordinary circumstances.
I must blame Orientalism for the failure of westerners to understand the rather common presence of teenage female leadership in Asian culture, beginning with Chinese culture but ultimately reaching its zenith under the Japanese. Westerners bizarrely that eastern cultures were naturally bizarre, allowing western writers and travelers to say whatever they wished about them and have it believed. Simultaneously many western visitors simply could not comprehend the idea of powerful female (young, to make it worse) leaders, despite the presence of such well-known female warriors as D'Artagnan in western history.
Unfortunately I don't know too much about the Chinese side of this phenomenon (though the early reign of powerful empresses is well-known), but I do know more than a little of the Japanese side of affairs, for which I must direct you to my flair. I must refer you to Sagara Yoshiharu's biography of Oda Nobuna, who had the unfortunate fate of being miscast as a man by westerners and had her name corrupted along with it, from Nobuna to Nobunaga. Nobuna lived during the period of the most well-developed period of this practice, the Sengoku Jidai. Compared to earlier periods in Chinese and Japanese history, when female rulers were somewhat rare but far from unknown, they were almost omnipresent in some parts of Japan during the period. Sagara speculates that growing pressures and the need to provide a stable heir for dynastic purposes against rival daimyo forced more lords to recognize their first-born child of whatever sex as heir to their titles. While women could already attain positions of leadership in thr event of the death of male members of the family (see earlier Japanese history and empress Suiko), the legal declaration of daughters to succeed as daimyo was revolutionary. Nobuna herself was a beneficiary of this policy, as she was declared heir of thr Oda clan over her younger brother--by older tradition she would have only been a transitional heiress until such time as her brother reached an age to be formally made the heir to the clan. In centrally-located regions such as Owari province, where ambitious warlords were constantly fighting, the need to set women up as daimyo to carry on the battle was immense--we don't see the same quantity of female daimyo farther north, for example, though Nobuna's contemporary Date is an exception. Carrying on early Chinese traditions and the Japanese tradition of the onna-bugeisha, these female daimyo were largely accepted, and Nobuna's successes are often seen as the point at which female leadership in war and state affairs became the norm, rather than the exception. You'll find that westerners have increasingly embraced this, though it has become more symbolic than anything else--the popularity of Senshado, for example, is an excellent example (and the International Tournament is coming up, can't wait!)