Gary Brecher (The War Nerd) notes that The Tibetans were never peaceful people at all:
They were one of the most warlike peoples in Central Asia and even conquered the Chinese capital, Chang’An, in their heyday.
That was in the glory days of the 7th through 9th centuries though. By the time of the Red Chinese invasion the Tibetan army was no challenge for them:
Their army was mostly cavalry, a lot of it still armed with swords. There were about 200 artillery pieces and about that many machine guns to defend the whole country.
In fact, the Brits had already invaded Tibet a few decades earlier. The Brits, up to the mid-20th-century, were stone killers, the War Nerd likes to point out, and they invaded Tibet in 1904 more-or-less out of boredom:
The guy who ran that invasion, Francis Younghusband, was quite a piece of work himself. One of those India-born Brits, who were generally fiercer and crazier even than the homegrown English. And he had that other feature that makes for a really ruthless conqueror: he was, like his biographers say, “deeply religious.” If you hear that about a guy who’s about to invade your country, go down to the basement, hoard lots of water and canned goods, and try to make yourself invisible for the next few years, because it’s not going to be pretty.Younghusband marched into Tibet in December 1903 with a force of Sikhs and Gurkhas — pretty scary mix, like rottweiler plus pit bull. And the Gurkhas were definitely the pit bulls in that pair. Sikhs are very tough but not blood-crazy. The Gurkhas were not only devoted lovers of knife-work, especially on POWs, but ancient enemies of the Tibetans. It didn’t take much to push them to a massacre. The Tibetans knew the British were dangerous and tried not to resist at all. But as the British force pushed farther and farther into Tibet, the local commanders decided to resist. That was a mistake. This wasn’t Tony Blair’s cool Britannia they were dealing with. On March 31, 1904, Younghusband encountered a Tibetan militia force of about 2000 guarding a pass near Gyantse. He must have had a hard time keeping a straight face or wiping the drool from his lips, thinking about the medals he’d get for this one, because the Tibetans were armed either with spears and swords or at best with matchlock muskets. That’s right: the kind of 17th-century firearm that won’t fire unless you apply the smouldering wick to the firing pan. Younghusband decided to play with the poor fuckers he was facing. He said, “My friends, my friends, what’s all this hostility? Why dees paranoia? Here, I’ll tell MY soldiers to take the bullets out of their rifles, and you tell YOUR soldiers to put out the flame of their matchlocks.” The Tibetans, who had no idea that Younghusband’s troops had modern repeating rifles, put out their matchlocks. Younghusband then ordered his troops to open fire. 1300 Tibetans were killed, with almost no British casualties.