Genesis 36

The genealogy of Esau (vs. 1-43)—There’s not a lot of action in this chapter. It simply records the genealogy of Esau. Some of Esau’s children were born in Canaan (v. 5), but he became very wealthy as well, and he moved south of Canaan. Apparently, at one point, he and Jacob tried to live together, but Esau “went to a country away from the presence of his brother Jacob. For their possessions were too great for them to dwell together, and the land where they were strangers could not support them because of their livestock. So Esau dwelt in Mount Seir. Esau is Edom” (vs. 6-8). Four times in the chapter it’s emphasized the “Esau is Edom” or “the father of the Edomites” (v. 43).

Edom was a mountainous region near the southern end of the Dead Sea; indeed, it was totally mountainous.  Sometimes the Bible refers to it as Mount Seir; in fact, it does so in Genesis 36:8.  In Numbers 20:18-21, they refuse to let the Israelites pass through their territory as Moses led the people to the Promised Land.  Then they disappear from Biblical history for about 400 years.  Saul and David both have victorious wars against Edom, and then later they unsuccessfully attack Israel during the reign of Jehoshaphat (2 Chron. 20:22).  They help Nebuchadnezzar besiege Jerusalem, and for this are roundly condemned by some of the prophets (notably Isaiah and Jeremiah).  The one chapter book of Obadiah is given totally to a denunciation of the Edomites for their treachery against Israel.  After helping Nebuchadnezzar, they settle in southern Palestine, where they appear to prosper for about 4 centuries.  However, during the Jewish revolt against the Greeks in the early 2nd century B.C., "they were again completely subdued, and even forced to conform to Jewish laws and rites, and submit to the government of Jewish prefects. The Edomites were now incorporated with the Jewish nation." —Smith's Bible Dictionary.  The whole region of Edom was full of caves and grottos, and that appears to be where many of the people lived. 

Some of their descendants remained into New Testaments times. They were no longer called "Edomites," but were known as "Idumeans;" they are never referred to with that name in the Old Testament. Herod the Great, the king when Jesus was born, and his family were Idumeans. Anyway, Genesis 36 gives us a long list of Esau’s offspring, especially those who ruled over the next few centuries.