Keith Laumer 
The Desert and the Stars [EPUB ebook] 

The Boyars have spent the past sixty years terraforming the planet Flamme, clearing jungle, descumming the seas, irrigating deserts and establishing forests. Now the Aga Kaga have decided to move in and claim it as their own. The Under-secretary of the CDT refuses to support the Boyars with anything more than a diplomatic note.

It’s up to Retief to deliver it and convince the Aga Kaga to abandon their claim. ‘Don’t worry. I’ll keep the peace, if I have to start a war to do it.’