This thing was evil in the eyes of God, so he struck Israel.
In context
5Joab gave the count of the people to David: all Israel numbered one million one hundred thousand men who drew the sword, and Judah numbered four hundred seventy thousand men who drew the sword. 6But Levi and Benjamin he did not count among them, for the king’s command was abhorrent to Joab. 7This thing was evil in the eyes of God, so he struck Israel. 8David said to God, “I have sinned greatly in doing this thing. Now, please take away the guilt of your servant, for I have acted very foolishly.” 9Yahweh spoke to Gad, David’s seer, saying,
