Where did Tibetan soldiers learn thier trade?

Did the Tibetan soldiers employ foreingers in their armies?

"Just before the downfall of Tibetan Dynasty, Tibetan governed Tibet, Qinghai, Silk-road, part of southern Xinkiang, part of central Asia. Tibet bordered with India, Tang, Persia, Mongolia. This was the largest area which was ever controlled by Tibetan. It had a population of 15 millions and an army of 400,000 strong (all estimates)."
http://cc.purdue.edu/~wtv/tibet/history.html#iif03

Did the Tibetans use only foreign war technology to gain strength in war?