Who did God tell Moses to vex and smite in Numbers 25?

The Midianites

(Because they vexed him with their wiles.)
And the LORD spake unto Moses, saying,

Vex the Midianites, and smite them:

For they vex you with their wiles, wherewith they have beguiled you in the matter of Peor, and in the matter of Cozbi, the daughter of a prince of Midian, their sister, which was slain in the day of the plague for Peor's sake. Numbers 25:16-18