The Sacred Armour of Antiriad

In The Sacred Armour of Antiriad, In 2086, civilization destroys itself in a nuclear Armageddon, as two factions who both develop an anti-radiation battlesuit completely immune to conventional weapons go to war against each other when diplomatic peace talks break down. In the following millennia, the survivors develop into a hardy but peaceful race, living a quiet agricultural existence. One day, mysterious alien forces emerge from an old volcano containing a prewar military base and attack, quickly conquering and enslaving the new breed of humans...