Scriptural analysis: The "adversaries" of Rezin are certainly the Assyrians, but the plural reference of this verse possibly refers to the defection of several of the rebellious states after the rapid entry into Palestine. Later a couple of them had renewed hopes in the rebellion, and once again joined with Rezin and Pekah, but their support was ineffective in stemming the tide. In the end, Rezin soundly defeated.
Historical information: The history of the Palestinian conquest by Assyria can be reconstructed from Assyrian documents as well as the references in the Bible. There were several participants in the rebellion of the Palestinian states against the Assyrians, including Rezin of Syria/Damascus, Hiram of Tyre, Pekah of Israel, Mitinti of Ashkelon, Samsi, queen of the Arabs, and possibly Hanno of Gaza. "Rezin of Damascus played a leading role in the rebellion. He thus figures conspicuously in the reports on other participants in the revolt, specifically Hiram of Tyre ad Mitinti of Ashkelon."
(Irvine, Stuart A. Isaiah, Ahaz, and the Syro-Ephraimitic Crisis. Scholar's Press. Atlanta, Georgia. 1990, p. 69)
"Ahaz of Judah was one of the few Palestinian rulers who did not join in the rebellion. In 734/733, he submitted voluntarily to Tiglathpilesar and paid tribute. The Assyrian records list this payment alongside the tribute of other states in the region." (Irvine, 1990, p. 70.)
The route of the conquest was south down the Eastern Mediterranean coast, with only brief skirmishes before arriving rather suddenly in Palestine. The sudden appearance led to the rapid acquiescence of several of the states in the rebellion, but Rezin, Hiram, and Pekah did not submit in this initial wave in 734/733 but held on for another two years. (Irvine, 1990, p. 70-71.)
"In 733/732, Tiglathpilesar campaigned in the southern district of Syria, defeated Rezin's army in the field, and besieged the capital city. Probably during the same year, Assyrian troops also took control of Syria's holdings in Bashan, Goln, and perhaps Galilee. Damascus fell in 732/731.Tiglathpilesar converted the whole of Rezin's extended kingdom into Assyrian provinces." (Irvine, 1990, p. 71-72) The action against Israel may have been minimal, but was concluded during the same time period.