King Shalmaneser V took over from his father Tiglath-pileser III in 726 BC. Hoshea might have thought this change in leadership would let Israel break free from Assyrian control. However, by not paying the yearly tribute, he provoked Shalmaneser's retaliation.
send envoys to King So of Egypt: Some scholars think the name So is short for Pharaoh Osorkon IV, who ruled from 730 to 715 BC. Others believe So refers to Pharaoh Piankhy, who ruled from 747 to 716 BC. They see the biblical name So as a Hebrew version of one of Piankhy's titles. Some suggest So is the city of Sais, the capital of Pharaoh Tefnakht, who ruled from 727 to 720 BC. Regardless of who this king was, it is clear Hoshea's hope for Egyptian support was a mistake.