Firemask: The Last Legion Book 2 by Chris Bunch
The Cumbre system is in a highly vulnerable position. Weakened in the aftermath of a vicious civil war, this collection of far-flung worlds is short on supplies and shorter on support. And the distant human Confederation government remains ominously silent. Now they stand in the path of an alien race bent on universal domination. Only the never-say-die members of the Legion stand in their way ...Previously driven from this planetary system, the alien Musth have returned in force. Outmanned and outgunned, the planetary government soon surrenders. Escaping capture, the surviving Legion soldiers scatter. Now, Garvin Jaansma and Njangu Yoshitaro conduct their own war - their way. Under their leadership, the troops take their fighting to the streets in a brutal guerrilla war against their oppressors - and against the odds.