During the divided monarchy, Judah and Israel were separate kingdoms. The Bible tracks the history of both. This is 2 Kings 15:32-33, telling us about Jotham's reign in Judah:
However, this is 2 Kings 15:30, telling us about events in Israel:
Now, one might immediately suggest that "the twentieth year" refers to the twentieth year of Jotham's life, rather than his reign. However, 2 Kings contains many verses of this form, and it's clear that they always refer to the time since the man's reign began, rather than the man's age.
This is not just my view. The NIV Study Bible places Jotham's reign at 750-735 B.C. and the death of Pekah at 732 B.C. But it also says:
One can certainly imagine the sort of intrigues that would make such events possible, and without more information, I don't see how a compelling case for this being an error can be made.
Updated: 2009-02-16