Complex sentence: Apart from threats within the ruling family, omnipresent challenges from the independent tribes of the interior rejected the authority of the sultan, recognizing the imam as the sole legitimate leader and pressing, by resort to arms, for the restoration of the imamate.
Split into simpler sentences: Apart from threats within the ruling family, there were frequent challenges from the independent tribes of the interior. The interior tribes recognized the imam as the sole legitimate ruler, rejected the authority of the sultan, and fought for the restoration of the imamate.