In Islam, one can NOT force a non-Muslim to convert and become a Muslim. We can only invite non-Muslims to Islam and inform them about the religion. It is very important to accept religion from your heart or else you won’t practice it routinely. It is like being forced into a marriage. If you do not like your wife and just married her for your parents sake or something, then you won’t accept her from the bottom of your heart. You won’t be able to love her. But the day you end up accepting her as your beloved wife, you will notice and cherish every little thing she says or does. You will want to be with her for the rest of yourlife. Same thing applies to religion. Till you don’t truly and deeply accept that “There is no god, but God,” you won’t be able to find peace even if you pray five times a day. However, it is permissible to fight or argue for the sake of religion when the opponent does something which is preventing Muslims from practicing Islam. Allah has taken all responsibilities towards protecting His religion, and He has been successful until now and He will do as He pleases. Therefore, fighting in Islam is the last way out and that too when Muslims are not allowed to follow their religion and in Islam one has to accept the religion from the heart before he/she starts practicing it.