Ayatollah Sistani elaborates what constitutes "loss of faith," which would make a Muslim's living in a non-Muslim country prohibited:

Religious Authority: 
Ali al-Sistanti
Fatwa Question or Essay Title: 
Ayatollah Sistani elaborates what constitutes "loss of faith," which would make a Muslim's living in a non-Muslim country prohibited:

Question: A believer residing in Europe, America and other similar countries feels estranged from the religious environment in which he was born and raised. Neither does he hear the voice of the Qur'an [recited from mosques] nor the sound of the call to prayer coming [from the minarets]; and there are no holy shrines, and their spiritual atmosphere, that he can visit. Is leaving such an Islamic environment of his country and its positive aspects considered "loss of faith"?

Fatwa: This is not the loss of faith that would make residing in a non-Muslim country haram (forbidden) for that person. However, staying away from such a religious environment may, with the passage of time, weaken the religious resolve of the immigrant to an extent that he may consider negligence of wajib (obligatory) deeds and committing of sins as insignificant. If a person has this fear that he might lose the faith in this manner, then it is not permissible for him to take residence in that country.