What are the lands of disbelief, and is it permissible not to pray in their mosques?

The abode of disbelief (Dar al-Kufr) is any land where the laws of disbelief are manifest and dominant. Prayer is obligatory upon a Muslim wherever he may be. If a mosque is found in the lands of disbelief, he is required to pray there with his Muslim brothers to attain reward. Prayer in the mosque is better for a man than his prayer at home, due to the Prophet's (peace and blessings of Allah be upon him) saying: "Congregational prayer is twenty-seven degrees superior to individual prayer," and his saying: "A man's prayer with another man is purer than his prayer alone, and his prayer with two men is purer than his prayer with one man, and the more numerous it is, the more beloved it is to Allah the Almighty." Some scholars have gone so far as to say that congregational prayer in the mosque is obligatory for men, except in case of a valid excuse. Others believe it is a condition for the validity of the prayer, and due to his (peace and blessings of Allah be upon him) saying: "Whoever hears the call [to prayer] and does not respond, there is no prayer for him except for one with an excuse."