If Muhammad(founder of Islam) never existed, would the world have been less violent?

You cannot undo history. You should realise that violence is a part and parcel of living not only for muslums but for the whole creation. Men kill men, animals kill animals, stars ram into other stars, black holes swallow up stars and galaxies. Look where you want and you will see that without violence there is no stability and peace.Muslims destroyed temples and idols because they do not believe in idol worship and they did this in places which they had conquered and annexed. This is what any victor in war is entitled to do and has been doing throughout history. Hence you do not have to single out Muslims for violence. Do you mean to say non muslim rulers did not kill their enemies in war? As far as crusades are concerned they were conducted by the Christians to fight against Muslims and rival christian sects. As for Muhammad(pbuh) is concerned he was not a military leader but a spiritual leader. He lead armies against those people who prevented him and his followers from following their beliefs; and for your info Hitler, Napolean, Lord Clive, Lord Dalhousie,were not muslims and were not taught by Muhammad(pbuh). Those who dropped atom bombs on Hiroshima and Nagasaki were not muslims and were not students of Muhammad(pbuh); those who faught wars in Vietnam, Iraq, and Afghanistan without any valid reason were not Muslims. (Did they find any weapons of m distruction in Iraq?).Those who slaughtered unarmed red Indians by the thousands and took over thier land were not Muslims; Those who killed black slaves by hundreds and burryied them under foundations of buildings were not Muslims but Americans. Were it the Muslims who performed a shameless show of bombings and destruction in Iraq over major TV channels? So my friend try to see the facts and speak the truth. I would advise you to take off your communal goggles and look at the world in proper prospective. It is not necessary to always be with the majority.