first of all -sorry for the english. I'm writing this from a computer in a village in Xinjiang,China..
What you are saying is grossly inaccurate: The Assyrians were renown for removing and destroying entire peoples.The Romans were quite lenient to occupied peoples within the oicumena (the helenist world),but they destroyed entire peoples in western Europe (Caesars occupation in Galia)
When we had a chance we were as nasty (King Davids exploits in book of Samuel,Alexander Yannai's forced conversion of the edomians).The christian were the first global monotheistic religion and they did destroy the entire population of Eastern and central europe (the area known as Prussia was settled by a slav tribe known as Prussians ,till the converted Eastern franks (germans) got to them .
Islam is probably no worse (and maybe a bit better) from anybody else on that list. And at leas the first Chalifs enforced an ethical conduct of war...