What it was. Egypt is the empire the Old Testament knows longest. The 1915 ISBE describes "the two lands" of the Nile valley and delta, a settled, monumental civilization already ancient in Abraham's day, fed each year by the river's flood and ruled by Pharaoh as a god-king (ISBE, "Egypt," I; III). Unlike the Mesopotamian powers that rose and fell, Egypt is a near-constant southern presence across the whole story: the land Abraham and Jacob go down to in famine, the house of bondage of the Exodus, and later the great rival and sometime-ally on Judah's southern flank. The ISBE arranges its dealings with Israel by dynasty, the oppression and exodus under the powerful XVIIIth–XIXth Dynasties (the Ramessides), then the later kings who meet Israel and Judah by name.
How it dealt with Israel and Judah. After the Exodus, Egypt and Israel meet again as kingdoms. Solomon married a pharaoh's daughter and received the town of Gezer as her dowry (1 Kings 9:16). Within a generation the Libyan pharaoh Shishak sheltered the rebel Jeroboam and then plundered Jerusalem (1 Kings 14:25). For the next three centuries Egypt is chiefly the southern counterweight to Assyria and then Babylon, a tempting ally for small kingdoms looking to revolt, and usually a disappointing one. The Cushite (Ethiopian) pharaoh Tirhakah marched against Sennacherib (2 Kings 19:9); Pharaoh Neco killed Josiah at Megiddo and briefly made Judah his vassal before Babylon broke him at Carchemish (2 Kings 23:29; 24:7); Hophra failed to lift Babylon's siege of Jerusalem (Jeremiah 37:5–8). Egypt's own independence ended when Persia conquered it in 525 BC (ISBE, "Egypt," II). (Source: ISBE 1915, "Egypt," with the named-king detail from the individual entries below.)