Who was Shallum?
Shallum was the 15th king of Israel, and successor of Zechariah, whom he publicly assassinated in the 7th month of his reign.
Nothing more is known of Shallum than that he was a son of Jabesh, which may indicate that he was a Gileadite from beyond Jordan. He is said to have made "a conspiracy" against Zechariah, so was not alone in his crime. The conspirators, however, had but a short-lived success, as, when Shallum had "reigned for the space of a month in Samaria," Menahem, then at Tirzah, one of the minor capitals of the kingdom, went up to Samaria, slew him and took his place.
It was probably at this time that Syria threw off the yoke of tribute to Israel (see JEROBOAM II ), as when next we meet with that kingdom, it is under its own king and in alliance with Samaria (2 Kings 16:5 ).
The 10 years of rule given to Menahem (2 Kings 15:17 ) may be taken to include the few months of military violence under Zechariah and Shallum, and cover the full years 758-750, with portions of years before and after counted as whole ones. The unsuccessful usurpation of Shallum may therefore be put in 758 BC (some date lower).
IBSE, "Isaac" (in the public domain) with minor edits.