Complex sentence: The 8th and 10th Indian Infantry Divisions, 2nd Indian Armoured Brigade and the British 4th Cavalry Brigade were all involved in the Anglo-Soviet invasion of Iran (August--September 1941), which was rapid and conducted with ease.
Split into simpler sentences: The 8th and 10th Indian Infantry Divisions, 2nd Indian Armoured Brigade and the British 4th Cavalry Brigade. Were all involved in the Anglo-Soviet invasion of Iran (August--September 1941), which was rapid and conducted with ease.