How the Disbelievers Manage to Encroach upon Muslim Lands

Imām Ibn Taimiyyah, may Allāh have mercy on him, said:

Among the things that lead to the disbelievers encroaching upon the lands of Muslims is the appearance of ilḥād,¹ hypocrisy, and bidaʿ.²

¹deviation from the truth and what’s right into disbelief, misguidance, or sinfulness (tr.)
²acts of worship invented by people, not legislated by Allāh (tr.)

Majmūʿ Al-Fatāwá, vol. 13, p. 180.