Complex sentence: Nagash eventually offered a truce with the Skaven, though: he would supply the Skaven with warpstone from Cripple Peak and in exchange, the Skaven would help Nagash with his plan.
Split into simpler sentences: Nagash eventually offered a truce with the Skaven, though: he would supply the Skaven with Warpstone from CripplePeak. In exchange, the Skaven would help Nagash with his plan.