What was the reason for the Prophet's (peace be upon him) command to emigrate to Abyssinia, despite it being a land of disbelievers, and is it permissible to use this as evidence for the permissibility of residing in lands of disbelievers?

First: The emigration to Abyssinia was due to the intensification of harm inflicted by the polytheists upon the companions of the Messenger of Allah, peace and blessings be upon him. It was a land where no one was wronged, and it was not an indication of absolute residence in lands of disbelief. Rather, it was a transfer from an oppressive land of disbelief to a land of disbelief where there was no oppression.

Second: The general rule for moving from the land of Islam to the land of disbelief is prohibition, due to the great harms it leads to, such as weakening the glorification of Islamic rituals, inability to manifest them, weakening loyalty to believers and disavowal of disbelievers, and its danger to Muslim youth. However, if necessity or a legitimate need arises, it is permissible under conditions: that one is secure in their religion, that loyalty and disavowal are firmly established within them, and that they are able to openly practice their religion.