Here is my thoughts. It’s going to be hard to keep this short.
The following I think has contributed to the spread of Islam:
1. According to the historic Muslim understanding, there is no separation between religion and government-what in Christianity would be called the separation of church and state. I am not speaking here of the secularist idea that the state should marginalize religion and discourage people from voting their consciences as Christians. We are talking about the idea that church and state are not the same thing and that they have different spheres of activity. Christians understood seperation of church and state from Christ himself, Matthew 22:21, in which Christ is quoted as saying: ‘Render therefore unto Caesar the things which are Caesar’s; and unto God the things that are God’s.’
2. Because of the need to expand God’s dominion by wars of conquest, Islam’s ideology imposes on Muslims the duty to fight for God’s community. This duty is known as jihad (Arabic, “struggle, fight”). French sociologist Jacques Ellul notes, “Jihad is a religious obligation. It forms part of the duties that the believer must fulfill; it is Islam’s normal path to expansion.”
3. In the seventeenth century it had begun to sink into Muslim consciousness that something was desperately wrong in the world. Though Muslim society had previously been more advanced economically and in some ways culturally than European society, it began to dawn on Muslim leaders that the barbarian infidels of Europe were catching up and in certain ways were ahead of Muslim society.
4. European domination of the Muslim world was short-lived, ending in the 1960s with the close of the de-colonialization that followed World War II. Yet it had an enormous effect on the Muslim psyche.
In conclusion, the Muslim mindset is trying to go back to the good old days. Where Muslims had a religious superstate. Anyone resisting would be dealt with. There is several history you can read on this.
Hope this helps.