Cast them down, etc. The prophet thinks of himself as not only the predictor, but the minister, of the Divine judgments. So it was given to Jeremiah (Jeremiah 1:10) "to root out and to pull down," and to Amos (Amos 9:1) to "smite" and to wound.
He executes the sentence, not on Egypt only, but on the other daughters of the famous nations, sc. on the nations themselves, especially those that are named in the verses that follow.