Complex sentence: Samaritans claim that they are descended from the northern Kingdom of Israel, which had parted ways with the southern Kingdom of Judah after the death of King Solomon (see 1 Kings 12).
Split into simpler sentences: Samaritans claim that they are descended from the northern Israelite Kingdom of Israel. There was a political division between the southern Kingdom of Judah and northern Kingdom of Israel, which took place after the death of King Solomon (see 1 Kings 12).