A lot of people try to paint an incorrect picture of Islam. They say Islam was spread through sword, that Islam forces people to become Muslim whether they like it or not.
Below are a few verses from the Qur'an.
1) "If it had been the will of your Lord that all the people of the world should be believers, all the people of the earth would have believed! Would you then compel mankind against their will to believe?" (10:99)
If it had been Allah's Plan or Will not to grant the limited free-will that He has granted to human beings, His omnipotence could have made all mankind alike: all would then have had faith, but that faith would have reflected no merit on them. In the actual world as it is, humans have been endowed with various faculties and capacities, so that they should strive and explore, and bring themselves into harmony with Allah's Will. Hence faith becomes a moral achievement, and to resist faith becomes a sin. As a complementary proposition, people of faith must not be impatient or angry if they have to contend against unfaith. And most important of all, they must guard against the temptation of forcing faith, i.e., imposing it on others by physical compulsion. Forced faith is no faith. They should strive.
2) "(O Prophet Muhammad) proclaim: 'This is the Truth from your Lord. Now let him who will, believe in it, and him who will, deny it.'" (18:29)
Our choice of free will involves a corresponding personal responsibility. We are offered the truth: again and again it is pressed on our attention. If we reject it, we must take all the terrible consequences that are prefigured in the fire of hell. Its flames and roof will completely enclose us like a tent. Ordinarily there is water to quench the heat of thirst: here the only drink will be like molten brass, thick, heavy, burning, sizzling. Before it reaches the mouth of the unfortunates, drops of it will scald their faces as it is poured out.
3) "If they turn away from thee (O Muhammad) they should know that We have not sent you to be their keeper. Your only duty is to convey My message." (42:48)
If the people do pay heed to the warning or reject it, Prophet Muhammad, pbuh, (or his followers) is not responsible for bringing about the penalty or for forcing people to come to the right path (Islam). He is not a guard set over them to free them from the need of exercising their limited free-will.
4) "Let there be no compulsion in religion." (2:256)
Compulsion is incompatible with religion because: (1) religion depends on faith and will, and these would be meaningless if induced by force; (2) Truth and error have been so clearly shown up by the mercy of Allah that there should be no doubt in the minds of any person of goodwill as to the fundamentals of faith; (3) Allah's protection is continous, and His plan is always to lead us from the depths of darkness into the clearest light.