Complex sentence: The Alans (Alani) were an Iranian-speaking subdivision of the Sarmatians which were split by the invasion of the Huns into two parts, the European and the Caucasian.
Split into simpler sentences: The Alans (Alani) originated as an Iranian-speaking subdivision of the Sarmatians. They were split by the invasion of the Huns into two parts, the European and the Caucasian.