[pavpanchekha]

It's not just massacres and brutality. Earlier societies had more acceptable political compromises. Look at the Russian war in their south. Grozny was carpet bombed to flat, but what ended the war was agreeing to substantial autonomy for Chechnya: in exchange for personal loyalty to Putin, Chechnya is allowed transfer payments, and Kadyrov (the ruler of Chechnya) has a personal police/army force. Dealing with guerilla warfare is easier if you mostly agree to their demands. If the US had agreed to let the North run Vietnam, the war would have been easy; if the US hadn't pursued de-baathization and left power structures in place, Iraq would have been easier as well. But of course you don't pursue regime change to lift the regime in place. Compare with Desert Storm, where regime change was not pursued.