The location of Midian has been identified based on epigraphic sources from the Second Temple Period, the Mishnaic Period, and the Talmudic Era, as an area of land on the northern part of the Arabian Peninsula. Over the years, Midianite groups migrated northward and settled in various places on the eastern bank of the Jordan River, some in the area of Moav.

We first encounter Midian as the name of a son of Ketura, Avraham’s second wife (Genesis 25, 2). Two generations later, a group of Midianite traders were involved in the selling of Yosef (Genesis 37, 18).

When Moshe fled from Egypt after killing the Egyptian man, he found refuge in Midian with Yitro the Priest of Midian. Moshe even marries Yitro’s daughter Tzipporah (Exodus 2, 15).
 

At the end of Bnei Yisrael’s desert wandering, the Midianites became foes of Bnei Yisrael, joining Moav in trying to curse Israel. They actively cooperated in the Sin of Baal Peor. Moshe sent 12, 000 fighters to take retributive action against Midian, and they killed five Midianite kings (Numbers 25; 31).
Apparently, the Midianites in the events of Bemidbar were Midianite groups in the region of Moav, and not the same Midianites as those in the Arabian Peninsula.
 

During the era of the Judges (Shoftim), the Midianites raided the Emek Yizre’el area and destroyed crops. Gideon fought against them and succeeded in defeating the Midianites and killing their leaders (Judges 6-8). In the wake of this defeat, they seem to have been significantly weakened—so much so, that after the time of Gideon, the Tanakh does not mention incidents connected with the Midianites.
 

Archeological research studies have traced the footsteps of the Midianites through unique pottery styles attributed to them, as well as a temple near the mines in Timna. Apparently the Midianites were involved in copper mining in Timna, either as miners in the mines or as transporters or copper from the mines to  markets throughout the Near East.

For more on Midian, see: Midian (in Moav).