Samuel R. Delany 
City of a Thousand Suns [EPUB ebook] 

The war was over. The great computer which had arranged and directed the complex military operations of that future nation was to be dismantled. But the computer had become expert in the science of self-defence…and it resisted. The government buildings were blasted. Rockets rained on the great city, and the Empire of Toromon, the first great hope of humanity after the millennia of radiation wreckage, faced disaster at the hands of a super-scientific monster of its own creation. But, unknown even to Toromon’s desperate leaders, was the fact that behind the berserk computer lurked the unearthly mind of a real enemy — a foe from the most distant realm of space, intent on making the Earth the first victim of galactic conquest.