Genesis 36:31

These are the kings who reigned in the land of Edom before any king reigned over the sons of Israel.

AND THESE ARE THE KINGS THAT REIGNED IN THE LAND OF EDOM. This was written in order to relate that the blessing of Isaac was fulfilled in Esau. He had said to him, And by thy sword shalt thou live, and they prevailed over the sons of Se’ir the Horite and reigned over them in their land. These cities mentioned here were provinces in the land of Edom, for Bozrah belonged to Edom, as it is written, For the Eternal hath a sacrifice in Bozrah, and a great slaughter in the land of Edom. Similarly, the land of the Temanites, is also of Edom, as it is said concerning it, And thy mighty men, O Teman, shall be dismayed, to the end that every one may be cut off from the mount of Esau, as are all the cities mentioned here. Scripture, however, relates that these kings did not succeed their fathers, as was the case in Israel.
The expression, Before there reigned any king, means “many years before.” But before there reigned any king does not mean that these kingdoms of Edom continued to exist until the kingdom of Israel. Instead, it means to say that at that time the Edomites will not have sovereignty, in order to fulfill Isaac’s words, and thou shalt serve thy brother. It is possible that all these kings had already passed away in the days of Moses, refers to Moses. This coincides with the opinion of Ibn Ezra expressed in his commentary on Verse 31. as they were old when they crowned them, and their lives were not prolonged.

לפני מלך מלך, before Moses arose as the saviour of Israel. All national heads of a people are automatically called “king,” regardless of their constitutional function. I have found in the historic writings of Josephus a list of about 40 such kings in Israel before the establishment of the Davidic dynasty.

ואלה המלכים, the Torah informs us that the Edomites had to appoint outsiders, members of other tribes, as their kings, seeing that they did not find a suitable personage for such a task among their own. Not only that, but none of the kings whom they did appoint raised a son fit to take over the position of king from his father.

לפני מלך מלך, before Moses was appointed leader of the Jewish people. Moses, as distinct from kings elected by the people, was appointed as such by G’d, as we know from Exodus 6,23 ויצום אל בני ישראל, “He commanded him to be the leader of the Children of Israel.” This expression is repeated in Samuel I 25,30 where Avigail refers to the time when G’d appointed David as king (נגיד) over the Jewish people. However, when the kings ceased ruling over the kingdom of Esau/Edom, they were replaced by leaders known as Alufim. It is reminiscent of the prophecy revealed to Rivkah in Genesis 25,23 ולאום מלאום יאמץ. [perhaps the author understood these words as distinguishing between the internal cohesion of the Kingdom of Edom at different times. Ed.]

ואלה המלכים, the kings of the nation Edom are mentioned at length in the Torah before any kings of the Jewish nation. According to what we read here eight kings and eleven Alufim ruled in Edom before the first Jewish king was crowned. The kings that ruled over Edom were not hereditary dynasties, i.e. father bequeathing his throne to his son, but the Edomites appointed outsiders as their kings. This was the basic difference between the power structure in Edom and that in the Jewish state afterwards. Even though the Edomites were politically organised, had experience in being ruled centrally by a king, this did not help them once the Jewish people began to be organised under the rule of kings. Already the very first of the Jewish kings, Sha-ul, fought a war against the Edomites, and the Edomites could not defeat him. King David, a few years later, totally subdued the Edomites, resulting in that nation being enslaved to Israel. This situation continued until the reign of Yehoram son of Yehoshaphat, (about 150 years later ) According to Bereshit Rabbah 83,1 this is the meaning of Proverbs 20,21 נחלה מבוהלת בראשונה ואחריתה לא תבורך, “an inheritance gained hastily at the outset, will not be blessed in the end.” The Midrash there also states that both the Edomites and the Israelites appointed eight Kings. The eight Edomite Kings were: Bela, Yovav, Chusham, Haddad, Simla, Sha-ul, Baal Chanan, and Hadar. The Jewish Kings were Sha-ul, Ish Boshet, David, Solomon, Rechavam, Aviah, Assa, Yehoshaphat, and during the reign of his son Yehoram the Edomites rebelled.