Invaders from the north?
Possibilities include Hittites (empire long destroyed before David), Macedonians (considered rough country cousins at best by the Athenians and other southern Greeks), several empires governed from Damascus, I will also add groups like the Huns and Mongols who would have approached by crossing the Caucus region.
I would agree there are many unexplained/uninterpreted old testament prophecies. But Jesus himself made it unclear that there are any "yet-to-be-fulfilled" prophecies:
"And when ye shall see Jerusalem compassed with armies, then know that the desolation thereof is nigh. Then let them which are in Judaea flee to the mountains; and let them which are in the midst of it depart out; and let not them that are in the countries enter thereinto. For these be the days of vengeance, that all things which are written may be fulfilled." (Luke 21:20-22 KJV)
>>>God is not yet done with the Jewish people or Israel.<<<
Paul didn't think so:
"For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh:" (Rom 9:3 KJV)
The apostles went way out of their way trying to beat it into our thick skulls that God is no respecter of persons:
"God that made the world and all things therein, seeing that he is Lord of heaven and earth, dwelleth not in temples made with hands; Neither is worshipped with men's hands, as though he needed any thing, seeing he giveth to all life, and breath, and all things; And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;" (Acts 17:24-26 KJV)
"Then Peter opened his mouth, and said, Of a truth I perceive that God is no respecter of persons:" (Acts 10:34 KJV)
"For there is no respect of persons with God." (Rom 2:11 KJV)
"And, ye masters, do the same things unto them, forbearing threatening: knowing that your Master also is in heaven; neither is there respect of persons with him." (Eph 6:9 KJV)
"But he that doeth wrong shall receive for the wrong which he hath done: and there is no respect of persons." (Col 3:25 KJV)
"My brethren, have not the faith of our Lord Jesus Christ, the Lord of glory, with respect of persons." (Jam 2:1 KJV)
"But if ye have respect to persons, ye commit sin, and are convinced of the law as transgressors." (Jam 2:9 KJV)
"And if ye call on the Father, who without respect of persons judgeth according to every man's work, pass the time of your sojourning here in fear:" (1 Pet 1:17 KJV)
"For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him." (Rom 10:12 KJV)
"There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise." (Gal 3:28-29 KJV)
"That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ." (Eph 2:12-13 KJV)
"Where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all." (Col 3:11 KJV)
There are more . . .
Philip