The Wizard of Linn (1962)

The second book about Clane - and this time he has an even worse problem.

The alien invading Riss that caused such problems for humans in the distant past are back, and humanity has a much lower technology level and little understanding of what they do have Clane excepted. Political infighting and his barbarian opponent all have to be dealt with if he is to have the slightest chance of saving them. Civilising politicians and barbarians might be harder than defeating alien invaders though.

http://baencd.thefifthimperium.com/13-TheBalticWarCD/TheBalticWarCD/Transgalacti...

http://freesf.blogspot.com/2009/08/wizard-of-linn-e-van-vogt.html ( )

This is a sequel to "The Empire of the Atom" in which Vogt introduced the world 10,000 years from now. It's world where bows and arrows and space technology live side by side.
Once mankind had a star-spanning civilization. But then the alien Riss came and their were desperate battles against them. Finally in resisting the Riss, mankind's great civilisation collapsed.
Mankind is consigned to using left-over, handed-down technology to allow the construction of space craft. The engineers are completely ignorant of the vast body of knowledge that underlies the apparently simple processes.
The Riss have returned and a much weaker human race must face them.
Lord Clane Linn must battle them to save all the planets on which humankind still survive. However he must also tame the ferocious warlord Czinczar, and concurrently defeat the murderous plots of the Lord Advisor and his hidden supporters. This is an above-average space epic with typical van Vogt flourishes. ( )