The land of Edom lay to the south-east of Israel.
There is a long history behind the antagonism between Edom and Israel which is reflected in Obadiah.
Impulsive Esau had sold his birthright to his scheming younger Jacob. Each were given new names, and these became the name of the two nations descended from them – Edom and Israel.
After the Exodus, the Edomites would not allow the Israelites to pass through their territory (Nu. 20:14–21; Jdg. 11:17–18). Saul had fought against Edom (1 Sa. 14:47), David had been victorious in battle over it (2 Sa. 8:13–14), and Solomon had occupied it (1 Ki. 9:26–28). During the reign of Jehoshaphat, Edom and others attacked Judah (2 Ch. 20:1–2). Edom was free of the yoke of Judah for some 40 years (2 Ki. 8:20–22; 2 Ch. 21:8–10). Edom was then recaptured (2 Ki. 14:7; 2 Ch. 25:11–12), while later Edom attacked Judah (2 Ch. 28:17), freeing itself from Judah’s domination. Later, Edom became first an Assyrian, then a Babylonian vassal. Thereafter, Edom was in decline. Some of its inhabitants were forced into southern Judea, in an area which became known as Idumea (a name based on the Heb. ‘Edom’).
(Based on NBD)