The King of Judah, Ahaz, invited the king of Assyria to fight against Israel [the Ten Tribes] and Syria. But the policy of Assyria did not change after that. Even though the original alliance was a success, the later king of Assyria just continued his war against Israel until he exiled Israel into the land of  Medea [East of Assyria]. After that the kings of Assyria just continued their old policy and then invaded Judah, and then finally tried to conquer Jerusalem itself. The event  the Assyria army being wiped out at that point is well known. But the fact that Assyria was first invited in by the King of Judah is less well known. [See Kings 16]

Be careful whom you ask for help from. Alliances are important but with whom to make an alliance is something not simple.  [Since reading Thucydides I have been aware of how important alliances are. But the events surrounding the fall of the Ten Tribes shows how much care  one needs in determining with whom to form an alliance. ]