War World is a series of collaborative science fiction books set in the CoDominium universe of Jerry Pournelle, some novels being co-authored by John F. Carr and Don Hawthorne, as well as Larry Niven and S. M. Stirling.
It has a thin but breatheable atmosphere; this and its distance from Byer's Star make surface conditions on most of Haven very cold and dry, so much so that initial habitation is limited to a single large valley at the equator.
Each volume takes place in roughly chronological internal order, but starting in different time periods (for instance, CoDominium: Revolt on War World, chronologically the last collection in the series, is set during the earliest years of human settlement on Haven).
The series is starting over with the publication of War World: Discovery (2010), edited by John F. Carr.
The new volumes include fresh stories intermixed with ones from the original series, providing a more complete look at the War World universe.