The story may be a bit more nuanced that that:
From a review of "Genghis Khan and the Making of the Modern World"
"Arguably, however, Genghis Khan and the Mongols were the dominant force that shaped Eurasia and consequently the modern world. Not for what they destroyed – though they wrought much destruction all over the continent – but for what they built. They came close to uniting Eurasia into a world empire, and in so doing they spread throughout it technologies like paper, gunpowder, paper money, or the compass – and trousers. They revolutionised warfare. More lastingly, in the word's of the author: ' ...they also created the nucleus of a universal culture and world system. (...) With the emphasis on free commerce, open communication, shared knowledge, secular politics, religious coexistence, international law, and diplomatic immunity.' ".
Again looking at history, I believe without war we wouldn't have technology. Most of the technology that we take as granted in the medieval period came from the Mongols, who because of war managed to gather together inventors from multiple countries and cultures and put them together. They took Chinese fireworks and Bronze Workers from Eastern Europe (I can't remember the country) and put 1 + 1 together, they built a cannon. They also committed many atrocities, however it was always the victims own fault, many times they killed the messenger, which the Mongol's invented their own postal service so they got pissed off at that and just besieged cities. Other times they were given fare warning, nearly always 'surrender and we'll let you live your lives as you always have', yet people refused. IIRC one time the citizens refused and killed the messenger, this one led to the Mongols diverting a river into the city and then slaughtering everyone.
The book I read (http://www.amazon.com/Genghis-Khan-Making-Modern-World/dp/06...) is a real eye opener. The man merely wanted to protect his own family, but betrayal after betrayal he ended up conquering most of the old world. The only reason he didn't take over all of western europe was because 'middle' europe was so poor they thought it was like what we imagine the third world. Aside from Europe they didn't invade most of Africa and India, this was purely because they couldn't ride their horses and didn't feel like invading.
Get dozens of book recommendations delivered straight to your inbox every Thursday.