In the days of Amraphel king of Shinar, Arioch king of Ellasar, Chedorlaomer king of Elam, and Tidal king of Goiim, these kings made war with Bera king of Sodom, Birsha king of Gomorrah, Shinab king of Admah, Shemeber king of Zeboiim, and the king of Bela (that is, Zoar). And all these joined forces in the Valley of Siddim (that is, the Salt Sea). Twelve years they had served Chedorlaomer, but in the thirteenth year they rebelled. In the fourteenth year Chedorlaomer and the kings who were with him came and defeated the Rephaim in Ashteroth-karnaim, the Zuzim in Ham, the Emim in Shaveh-kiriathaim, and the Horites in their hill country of Seir as far asEl-paran on the border of the wilderness. Then they turned back and came to En-mishpat (that is, Kadesh) and defeated all the country of the Amalekites, and also the Amorites who were dwelling in Hazazon-tamar.
Then the king of Sodom, the king of Gomorrah, the king of Admah, the king of Zeboiim, and the king of Bela (that is, Zoar) went out, and they joined battle in the Valley of Siddim with Chedorlaomer king of Elam, Tidal king of Goiim, Amraphel king of Shinar, and Arioch king of Ellasar, four kings against five. Now the Valley of Siddim was full of bitumen pits, and as the kings of Sodom and Gomorrah fled, some fell into them, and the rest fled to the hill country. So the enemy took all the possessions of Sodom and Gomorrah, and all their provisions, and went their way. They also took Lot, the son of Abram's brother, who was dwelling in Sodom, and his possessions, and went their way. – Genesis 14:1-12
This passage is important for historical reasons. This bursting in of people and times is meant to locate these events into a specific time that this portion of the land might remember (similar to Isaiah 6:1).
In terms of practical usefulness, it is quite impressive the list of kings and the presumed force of even these early armies. But what is more impressive is the way in which Abram, the forefather of the conquering Israel, with his mighty men will defeat all of these kings. Likewise also, many kings will reign in the land when Joshua and the people come through and conquer. Even more so were there kings when Jesus Christ conquered the world.