This is book 1 of the Chaoswar Saga,

In the years following the Serpentwar, the Empire of Great Kesh was peaceful but dark clouds are gathering once more. An attack is all but certain. As his legendary ancestor had done, Martin conDoin, must defend the lands against invaders. Unlike his ancestor, his army is only old men and boys.

Pug, Midkemia's most powerful magician senses a growing darkness that spells his world's end. Soon the defenders will question everything they held dear including the loyalty of the defender's son Magnus.

Feist has taken his fantasy universe into a new phase with evocative characters and action that guarantees a page turner. The master retains his touch. ~~ Pam Allan