en_tn_condensed/jer/15/04.md

I will make of them

The word "them" refers to the people of Judah, not to the four groups listed in the previous verse. Yahweh is going to use the Gentile nations to punish Judah. This would have been very offensive to the Jews. They would have also been surprised to learn that Yahweh was using the Gentile nations.

because of what Manasseh ... did in Jerusalem

"because of the wicked things that Manasseh ... did in Jerusalem". Manasseh was a very wicked king who did many evil things.