Discworld 21: Jingo by Terry Pratchett

It isn't much of an island that rises up one moonless night from the depths of the Circle Sea -- just a few square miles of silt and some old ruins. Unfortunately, the historically disputed lump of land called Leshp is once again floating directly between Ankh-Morpork and the city of Al-Khali on the coast of Klatch -- which is spark enough to ignite that glorious internationalpastime called "war."

Pressed into patriotic service, Commander Sam Vimes thinks he should be leading his loyal watchmen, female watchdwarf, and lady werewolf into battle against local malefactors rather than against uncomfortably well-armed strangers in the Klatchian desert. But war is, after all, simply the greatest of all crimes -- and it's Sir Samuel's sworn duty to seek out criminal masterminds wherever they may be hiding ... and lock them away before they can do any real damage. Even the ones on his own side.