Aramaeans originally heralded from the Jebel Bishri hinterland, between the Euphrates and the site which was later the great caravan city of Tadmor (aka Palmyra). It is unclear why Aramaeans thrust toward the Euphrates, but it was likely due to their deforestation of the Jebel Bishri and the resulting soil erosion and rapid run-off of formerly trapped storm rains.
According to Tiglath-Pileser I, the Aramaeans crossed the Euphrates into Assyrian territory. They settled along the Euphrates from the Babylonian border to Carchemish. Noting the importance of the Euphrates as an artery, Tiglath-Pileser I drove the Aramaeans back after crossing the Euphrates on goat-skin rafts.
As the Aramaeans settled, first in Syria, they coalesced into kingdoms. One such kingdom was encountered by King Saul of Israel just before 1,000 BC. However, the Aramaeans in Syria were establishing themselves; this allowed Israel to form treaties with somewhat centralized authorities. Conversely, Aramaeans in Mesopotamia and east of the Euphrates were still nomadic peoples with no central authority; this made them a destabilizing force that could not be diplomatically addressed. By the second half of the 10th century BC, however, Aramaeans in Mesopotamia had settled enough to cooperate with Assyrian king Ashur-dan II (934-912) and Assyrian prosperity returned.