The LORD did not just establish David’s authority over Israel, but David, whenever he went to war against another people around him, defeated them, because the LORD preserved David wherever he went. In the ancient days, when one people was defeated by another, life went on as it always had, but they paid the conquering king tribute. The defeated king was obligated to send a set amount annually to the conquering king. The defeated king obtained this amount by taxing his own people (usually).
So David received tribute from the Philistines, from the people of Ammon, which was where the western portion of the nation of Jordan is today (Ammon is the name of the capital city of Jordan, even today); from the Amalekites, and from Edom and Moab, which is today partly in the nation of Jordan and partly in the nation of Saudi Arabia. These are the nations which paid David tribute, which immediately surrounded Israel.
David also defeated the Syrians, when a conflict arose between them. Syria was a great nation in ancient days, stretching from the Ammonites’ and Edomites’ and Moabites’ eastern borders, nearly to the Euphrates River. It encompassed modern day Syria, parts of Jordan, and much of Iraq.
There was more than one kingdom of Syria. The capital of one of the kingdoms of Syria was at Damascus, as it is also today. The capital of another kingdom of Syria was at Zobah. No one is certain today where Zobah was in ancient days, but Zobah was a powerful kingdom in ancient days, and is also mentioned in cuneiform tablets and the annals of the Assyrian kings.
David defeated the Syrians of Zobah first, then the Syrians of Damascus when they came to Zobah’s aid. When he received tribute from them, he was in effect reigning from the Mediterranean Sea to the Euphrates River, and so partially fulfilled the promise of God to Abraham:
On the same day the LORD made a covenant with Abram, saying: “To your descendants I have given this land, from the river of Egypt to the great river, the River Euphrates—” Gen 15:18
David partially fulfilled this promise, as a prophecy of Messiah, for David is a type of Messiah in His second coming as reigning king; for when Messiah Yeshua returns, He will completely fulfill this promise, and the borders of Israel will stretch from the Mediterranean to the Euphrates.
Syria has been making war on modern Israel and threatening her borders since Israel became a nation in 1948. But if I were Syria, I would tremble, because prophetically Syria always comes out on the bad end of conflicts between Israel and Syria. In fact, one of the yet to be fulfilled prophecies of Isaiah states:
The burden against Damascus.
“Behold, Damascus will cease from being a city,
And it will be a ruinous heap.
The cities of Aroer are forsaken;
They will be for flocks which lie down, and no one will make them afraid.” Isa 17:1-2
Damascus has never been a ruinous heap, from the day that it was founded to this day. But if it continues to pursue its war against Israel, as it will, the word of the LORD will come to pass upon it, and the prophecy of David’s victory over it will be fulfilled in Messiah Yeshua, when He comes to reign in Israel.