What does Judges 12:2 mean?
The men of Ephraim have arrived on the east side of the Jordan River, in the territory of Gilead. They are armed and ready for battle—but the fight with the Ammonites is over (Judges 11:32–33). Jephthah has led the people of Gilead and greater Manasseh to victory, pushing the Ammonites out of Israel's territory. The men of Ephraim claim to be furious they were not invited to the war. They are so angry, in fact, they threatened to burn Jephthah inside his own house (Judges 12:1). This resembles a similar incident where Gideon had to deal with angry Ephraimites during his war against Midian (Judges 7:24; 8:1–3).Jephthah's response is simple enough, though the text does not explicitly indicate whether it's true. He claims Gilead did call on the Ephraimites for help while the Ammonites were oppressing them. The men of Ephraim did not come and save them, either before (Judges 10:17–18; 11:4) or during the decisive battle.
The greater point being made here is that Gilead—not Ephraim—was under the worst threat. The Ammonites were on the verge of driving them from their own territory east of the Jordan. If Ephraim wanted to help Gilead, they could have responded to the call for help at any time. Rather than taking this well, the Ephraimites will escalate through insults and spark a minor civil war (Judges 12:4–6).