Dude there are certain concrete differences b/w two eg islamic political system puts certain religious responsibilty on political head of state ( duty of promotion, observance and defense of religion, caliph is temporal as well as spiritual head)... But western systems don't, monarch, pm or president are just temporal head.
It is the islamic system that gave people right to elect their caliph through advisary council of the best among them... It was a new idea that time while west adopted it in 17th century.
Islam gave final blow to theory of divine right when caliph Abu Bakr assumed caliphate and renounced hashmites right. And upheld the principle of islam that caliph is not a family post. It was new idea that time. While west was naive to this til 17th century n Thomas Hobbes' Leviathan was defending it and john Lock introduced this concept in europe at the end of 17th century. So it was the islamic concept adoptd by the west.. And it is the tenet of islamic system adopted by the west.
Islam allows that head of state to be appointed on religious idetity a black slave can be appointed a caliph... ( ie an arab caliph for whole islamdon or a turk) bt a nomuslim citizen can't be.
In west , the emphasis is on citizenship not on religion...
( however i confess islamic system onces the most liberal system is now somewhat a redundent concept and has ancient look it is due to the fact it was not allowed to evolve due to untimely death of caliph umar, and worldly ambitions of Rashidun Successors.) bt islamic system is a reality you can't renounce its existence.