In those days i.e. towards the end of Jotham's reign. The Lord began to send, i.e. disposed their hearts to unite their forces together, and to make preparation for a war against Judah; which yet they did not execute till Ahaz's reign.
Related Commentaries of 2 Kings 15:37
2 Kings 15:37
37 In those days the LORD began to send against Judah Rezin the king of Syria, and Pekah the son of Remaliah.