I must have read Space Viking over a hundred times. Since my youth, H. Beam Piper's Terro-Human histories, as well as his Paratime novels, have thrilled me.
Space Viking lays out Piper's Terro-Human universe several generations after the collapse of the Federation, a galaxy spanning human government. Civilization, across space, is slowly reverting to barbarism, except a few worlds that've held on.
The Sword Worlds struggle on but they are unwittingly watching their chances at a civilized future slip away. Pirating former colonized worlds for goods and treasure has left the Sword Worlds uncreative and culturally parasitical. Few realize the doom looming on the horizon but when a madman kills Lucas Trask's fiancé, Trask's quest for vengeance becomes instead a movement for hope.
I love H. Beam Piper and can't recommend Space Viking highly enough.