The men of Ephraim gathered themselves together - ויצעק vaiyitstsaek, they called each other to arms; summoning all their tribe and friends to arm themselves to destroy Jephthah and the Gileadites, being jealous lest they should acquire too much power.
Compare the similar complaint of the Ephraimites to Gideon Judges 8:1, when a civil war was only avoided by Gideon‘s wise and patriotic moderation. The overhearing pride of Ephraim comes out in both occurrences (see also Joshua 17:14-18).
We will burn thine house upon thee with fire - Compare the fierce threat of the Philistines to Samson‘s wife Judges 14:15, and the yet fiercer execution Judges 15:6. Burning appears as a mode of capital punishment Genesis 38:24; Joshua 7:25, and as a mode of desperate warfare (Judges 1:8; Judges 20:48; Joshua 8:8, Joshua 8:19, etc.).