Is the land of the Muslims considered one entity regarding the obligation of jihad?

Question:
He says: Honorable Shaykh, may Allah grant you success, is the land of the Muslims considered one entity in this time? If the enemy attacks one of them, is it obligatory for all Muslims to fight in jihad?

Answer:
My brothers, since a long time ago, the land of the Muslims has been divided into states and emirates, and each state has its own ruler, its own imam, and its own subjects. It is not obligatory for our subjects to obey an imam in another subject's domain. This is the practice that the Muslims have followed. They have their ruling, and we have our ruling. However, assisting them with money, or assisting them by volunteering in jihad with them, is permissible. But that it is obligatory upon us? It is not obligatory upon us. We defend our land, our land. This is what is obligatory upon us; it is an individual obligation (fard 'ayn). As for our fighting for other Muslim lands, that falls under the category of volunteering. Yes.