Mohammed was in no way to be held to such a promise as the one made in the first place, because the quarrel was in essence superficial. Killing It seems to be a popular thing now to say that killing should never be condoned within society. Yet Robbespiere of the infamous French revolution held in high esteem the innovators of such a theorem. Lennon preached atheism but found it necessary to kill his opponents. Stalin had many killed based on his Atheistic principles.
All religious beliefs have bloody history.
How harshly were the German people treated by the allied people after World War Two. Your secular humanist principles can be argued against with the same arguments you use against Islam. I cannot say but who can. Such an obscure and removed history cannot be used to judge the truth. We only know speculative information concerning the Roman emperors and that was in a highly literate society, even many slaves could read.