What does Judges 12:1 mean?
The tribe of Ephraim is ready to fight about not being invited to join the conflict with the Ammonites. A similar confrontation happened with Gideon after the route of the Midianites. The fighting men of Ephraim were called at the last minute to cut off fleeing enemy soldiers (Judges 7:24; 8:1–3). Here, again, the tribe appears more motivated to bicker with their own people than they are to seek out their true enemy.The war with the Ammonites is over (Judges 11:32–33). Yet the men of Ephraim cross the Jordan River into the territory of Gilead armed and ready for battle. Scholars believe Zaphon was located just east of the Jordan, about halfway between the Sea of Galilee and the Dead Sea. There they found and confronted Jephthah.
It's unclear why the men of Ephraim are so upset about being left out of Israel's victory. It may be that their land was also attacked by the Ammonites at one point (Judges 10:8–9), though it was not occupied. It may be that missing the war meant missing the opportunity to partake in the spoils of battle. Or this might simply be another thin excuse (Judges 11:13) from a group eager for conquest. Rather than celebrating the end of Ammonite oppression, Ephraim threatens to burn Jephthah's house down with him in it.