C. F. Keil and Franz Delitzsch on Judges 11:8

Jdg 11:8

The elders replied, “Therefore (לכן, because we have formerly done thee wrong) we have now come to thee again to make thee our head, if thou comest with us and fightest against the Ammonites.” The clauses והלכתּ, ונלהמתּ, and והיית, which are formally co-ordinate, are logically to be subordinated to one another, the first two expressing the condition, the third the consequence, in this sense, “If thou go with us and fight, ... thou shalt be head to us, namely, to all the inhabitants of Gilead,” i.e., to the two tribes and a half on the east of the Jordan.