Gordon R Dickson 
None But Man [EPUB ebook] 

The Frontier Rebellion has long been won, thanks in part to the efforts of Culihan O’Rourke, the best hijacker the Rebels ever had. When he is greeted upon his return to Earth with beatings, torture, and interrogation, Cully learns the hard way of the ultimatum issued to Earth by the Moldaug: evacuate the Frontier or be destroyed.