Semper Fi: The Empire's Corps, Book 4

Two years after the empire abandoned them on Avalon, Colonel Edward Stalker and his marines have established the Commonwealth, a union of worlds intended to take the place of the vanished empire.

But now contact has been made with a remnant of the empire, a successor state controlled by a ruthless dictator bent on crushing the Commonwealth and expanding her rule over the entire galaxy. While the Commonwealth frantically prepares for war, a small team of marines is dispatched to the enemy homeworld with orders to bring down the dictator - by any means necessary....