What does 2 Kings 13:9 mean?

Jehoash, son of Jehoahaz, started ruling over Israel in Samaria during the thirty-seventh year of Joash, king of Judah. He was king for sixteen years. 2 Kings 13:9 - Modern Text Bible

(This verse introduces Jehoash as the next king of Israel, again tying his reign to the timeline of Judah's king.)