H. Beam Piper
Ace Books 
Synopsis: The Federation has fallen, civilization collapsed and high technology is preserved on only a few worlds, among them the Sword Worlds, home of the Star Vikings, who prey on weaker worlds as their namesakes preyed on weaker communities in Europe. On one such Sword World, Gram, Lucas Trask, a noble, gets married. Less than an hour after his wedding to Elaine Karvall, Trask is badly wounded and his new wife is killed by Andray Dunnan, a mad would-be suitor of Elaine’s. Dunnan escapes immediate vengeance by fleeing Gram, stealing the starship Enterprise [no relation]. Trask, who up until now has seen the activities of the Star Vikings as draining the Sword Worlds of vital skilled labour, no longer cares about the larger picture and only wants revenge. He stakes his holding to pay for a new ship, the Nemesis and sets out to find and kill Dunnan.
Repelled by the waste and horror of the activities of the Star Vikings, Trask soon changes the focus of his activities from raiding to civilization-building on Tanith, the world the Enterprise was intended to conquer and colonize. This is despite his various successes at raiding: he quickly acquires numerous allies. His desire for immediate revenge is frustrated by the scale of the Old Federation, 200 billion cubic light years, and the limited speed of starships, about 1 ly/day: it is possible for Dunnan to evade Trask until both are dead of old age.
Investigating a possible lead, Trask rescues the Victrix, of Marduk, bearing Prince Simon Bentric, who is only three lives away from the throne of Marduk. The Victrix is under attack by a known close friend of Dunnan, in the Enterprise and in the course of the rescue both the Enterprise and a ship allied to it are destroyed. Trask travels to Marduk with Bentric, and establishes close ties with the constitutional monarchy there.
Soon after, a local political extremist wins a plurality of the seats in Marduk’s parliament. Various elements of the Royal family flee to Tanith. News arrives that the extremist has staged a coup and is disposing of his political opponents. The King of Marduk is a prisoner, perhaps mind-controlled through torture and drugs. Trask and allies stage a counter coup, at great cost to the civilian population: some of the allies are Star Vikings along for the loot, although at least no planet busters or hellburners are dropped. The royal family is placed back on the throne of Marduk and it is clear elections are discontinued until the electorate is ready for them again.
Dunnan proves to have been the money behind the throne. Still on Marduk, he is tracked down and executed by Trask. Trask realizes he has greater things to devote his life to than revenge and vows to set up a League of Civilized Worlds.
Note: a lot more happens than the above suggests. There’s a dim outline of a romance, for one thing.
This is still a page turner twenty odd years since I first encountered it, although the scenes of mass destruction and slaughter are a lot more repulsive than they were to me then: Trask must kill millions of people in the course of tracking down Dunnan, given the scale of the weapons used and the fact that they are used on cities. Piper isn’t unaware of this, either. He deliberately draws a parallel between Trask and some poor bastard whose wife Trask has caused to be killed by his decision to raid that fellow’s world and when Trask is talking to a little girl, he wonders how many little girls like her his activities have killed.
There are the usual Piper views on politics and economics. I am not sure if the phrase ‘comparative advantage’ had any meaning in the Federation or after, since worlds industrializing ‑reduce- their demands for foreign goods [More obvious in Junkyard Planet, I will admit: Trask actually sets up trade routes at one point and there’s an ethnic group nobody likes who trade rather than raid].
There’s the ‘emigration saps home countries of good genes’ nonsense, on which the decadence of the Sword Worlds is blamed. There’s a general rejection of governments as useful tools of policy. It often surprises me Piper’s work isn’t the cause of as many Usenet arguments as RAH, although I suppose HBP’s obscurity and the way many of his odder beliefs are ego-strokers for colonials might go some way to explain that.
Despite his twitches, Piper spins out an interesting tale and the novel leaves the hope that perhaps Trask can make up for his atrocities if the League of Civilized Worlds is successful1. It is worth pointing out that where Trask is regrettable, Dunnan is even worse: Dunnan’s people drop hellburners on worlds, to deliberately kill local civilizations [Hellburners are H‑Bombs which burn for hours] out of spite whereas Trask is motivated by mere greed and a desire for vengeance and limits his collateral damage thusly: you can’t raid a 500 km-wide burnt spot.
BTW, has a country with a long history of constitutional monarchy and parliamentary rule ever fallen to a Hitler-esque coup as in TSV?
Piper stopped writing due to an entirely avoidable set of circumstances: his agent died, leaving poor, perhaps non-existent records of what was owed Piper. Lacking funds to feed himself and unaware he had actually sold at least one book for which money was owed him, Piper shot himself rather than be a burden to his friends, successfully avoiding a potential short-term cost to society at the definite cost of losing all of his possible future productive output [Piper could have easily lived until the present day]. After his death, his estate was eventually owned by the state of Pennsylvania. Ace Books then purchased the full rights to his books in the 1970s but after reprinting many of them, ceased production of most Piper titles and have shown little interest in selling the rights to the currently out of print title to another publisher, aside from licensing Old Earth Books to reprint Murder in the Gunroom , a mystery. Until Ace relents and either reprints or sells the rights, the only Piper books people are likely to be able to easily purchase new are The Complete Fuzzy and MitG. This is a great pity, as Piper was a solid writer who would be likely to appeal to a variety of audiences, not least Baen Books readers.
1: Although if one reads the later stories in this universe, the LCW is never mentioned again. Bad luck, King Trask.