Is it a duty for able Muslim men to implement shariah in whatever country they are in?
Brothers have told me it is obligatory.
Yes, shariah is meant to rule the entire world.
[22:64-65] To Him belongs everything in the heavens and everything on earth. Absolutely, Allah is the Most Rich, Most Praiseworthy. Do you not see that Allah has committed in your service everything on earth?
[31:26]To Allah belongs all that is in the heavens and the earth. He is the Rich, the Praised.
[57:10] And what cause have ye why ye should not spend in the cause of Allah?- For to Allah belongs the heritage of the heavens and the earth