Columbia subject headings:
Harvard subject headings:
Caliphs--Biography.
Islamic Empire--History--622-661.
Leadership--Religious aspects--Islam
ʻUmar ibn al-Khaṭṭāb, Caliph, -644--Psychology.
Princeton subject headings:
Command of troops--Religious aspects--Islam.
Leadership--Religious aspects--Islam.
ʻUmar ibn al-Khaṭṭāb, Caliph, -644.