Complex sentence: All of Afghanistan's immediate preceding rulers save Habibullah's father had died of unnatural causes, and his own immediate relatives being pro-German while he allied with Britain gave him justifiable grounds to fear for his own safety and his kingdom.
Split into simpler sentences: All of Afghanistan's immediate preceding rulers save Habibullah's father had died of unnatural causes. The fact that his immediate relatives were pro-German, while he was allied with Britain, gave him justifiable grounds to fear for his safety and his kingdom.