Why was Abraham afraid?

Sodom's army, and those of her four smaller allies, lay destroyed in the Valley of Siddim. The settlements of the giants East (from North to South) of the Jordan valley were in ruins never to recover (Joshua encountered only the last of them, Og the King of Bashan, more than five hundred years later). The Amalekites southwest in the Negev would eventually recover to harass Israel, but for now they were decimated.

Salem had been spared.

Abraham, with an army of 318 trained men (no word on casualties) and local Amorite allies had just eliminated the (likely) much larger raiding force from the lands around later Babylon and Persia, which had taken at least a year to raise. No word on how many had fled (if any), including the four kings themselves, but it had been an unqualified victory.

Abraham recovered everyone that he and Sodom and the other cities had lost. Abraham had the blessing of the remaining city of size in the area (Salem). Sodom, the ruined large city of the region was in his debt.

Abraham was now the dominant military power in the region, such that he spoke for his Amorite friends in dividing the spoils recovered from Sodom, and the king of Sodom was trying to entice Abraham away from a presumed tenancy covenant with the king of Salem.

Abraham is afraid.

The Lord comes to him in a vision telling him not to be afraid: God is his shield, and his reward.

Reward may be understandable, in light of Abraham refusing to take the spoils of war, but why is he of all people afraid?

We enter into some realm of speculation, trying to piece together a picture from a few scattered words and phrases.

A couple points:

1) The armies of Shinar and her allies bypassed Abraham, and Salem, on the way to Sodom. They hit the Amorite settlement, however. Then, on their way north, on the West side of the Jordan, they bypass Abraham and Salem again. Abraham has to chase them before he catches up at Dan.

God was with Abraham, and evidently Abraham and his allies were sufficient to route this enemy. The action is straightforward and simple.

But twice, notice, despite hitting every other people in the region, they had bypassed Salem and Abraham.

These are ancient armies, with poor logistics, such that the Bible makes particular mention that they captured the food stores of Sodom. They would need this for the trip home. Lot's flocks went too.

Abraham was at least as rich Lot, certainly richer. He might have hid in the city, but his flocks would have been ripe picking on the outside. He was left alone and only found out about Lot's capture after the armies were on their way out of the land.

This makes sense if Abraham and Salem had previously been considered "friendlies" to the raiding armies. Abraham had no reason to attack them until he found they had taken Lot. Abraham then attacked those "friendlies". It is possible that Abraham, if word of his betrayal got back to Shinar and further armies were raised for retribution or an occupying conquest, would now be a priority target by the dominant peoples in the greater region.

If there were other cities to the north that were allied with the lands of those four kings, it is possible they would be closed to Abraham if not outright hostile.

Jacob faced a similar, though more local situation, when his sons betrayed their family's covenant with Shechem, slaughtering their men and taking captive the survivors, so that he would be pariah in the region that the other cities would ally to destroy him.

2) Abraham was careful to refuse anything from Sodom, except for the 10% given to Melchizedek, king of Salem, and the share due to the Amorite Mamre and his brothers and (presumably) their fighting men under them. This may indicate an existing covenant between Salem and Abraham, whereby (as was common) Abraham made use of surrounding lands for his flocks while providing defense (and 10% of any spoils) to the city and king.

However, if Abraham's refusal of Sodom's apparent generosity is more than simply refusing the gifts of wicked people, but an awareness of Sodom hoping to secure Abraham's protection for themselves, his refusal may not have defused any suspicion on Melchizedek's part about Abraham's loyalties and/or offended the king of Sodom. A delicate political balance may have been temporarily upset.

Bear in mind that, while Hebrews makes favorible comparisons of Jesus our High Priest to Melchizedek's royal priesthood, such comparisons don't necessarily extend to every part of Melchizedek's life. That his lineage and descendants are not recorded doesn't mean he was actually without parents, for example. While he makes a useful picture, he himself may not be as righteous as we are tempted to believe simply because of Hebrews' mention.

Then again, he may be an excellent prototype of Jesus because he in fact was righteous. We just don't know much of anything about this ancient king or his relationship with Abraham.

3) Heavier on Abraham's heart, of course, was that anything Abraham gained in the land had not secured any real future for him or his people. If he held out until his death, everything would still dissolve then. There is a long term security issue here, and after God assured His protection he focused on a promised heir. Yet not only would Abraham be protected, but God was giving him a future and he would beget peoples who would cover all that lands around, even north and east ward to the border of Egypt and to Shinar at the Euphrates.