Albert Barnes Commentary Ezra 9:1

"Now when these things were done, the princes drew near unto me, saying, The people of Israel, and the priests and the Levites, have not separated themselves from the peoples of the lands, [doing] according to their abominations, even of the Canaanites, the Hittites, the Perizzites, the Jebusites, the Ammonites, the Moabites, the Egyptians, and the Amorites." — Ezra 9:1 (ASV)

Abominations - The mixed marriages had prevented that complete separation of the people of God from the idolatrous rites, or “abominations,” which the Law required, and which was necessary for purity of religion. See 1 Kings 11:2 note.