It is a space opera setting where colonies have been established on planets around the universe that are connected by wormholes. Space travel is conventional thrust except for those. Space weapons are mostly pointless after an arms-race involving ballistics was halted by an energy-shielding system, and then an arms-race involving lasers was halted by a conversion system that turns them into just more energy for the defender's shields. The wormholes are natural chokes into each system with no reasonable travel method existing outside of finding another wormhole outlet. Invasion and defense tactics are oriented almost entirely around taking and holding the wormhole entrance.

The main story centers around an important family on a planet called Barrayar. The planet was lost to the rest of the galaxy several centuries before when their wormhole turned out to be unstable and collapsed. The humans living there were in the earliest stages of terraforming and when they were cut off from the rest of the galaxy they were on an urgent clock to do the best they could to finish their work and make their now only planet permanently habitable. This meant not caring about anything but making it as Earth-like as possible, so they destroyed all existing plant and animal life in their speed (which wasn't the original plan).

The desperate expenditure of resources meant they had to settle for a very meager subsistence after a short while and their civilization downgraded to approximately the European dark ages for many generations.

They were inadvertently re-discovered by a race of humans called the Cetagandans who were mapping out new wormhole paths after this time, and within a few years they were invaded by the same who saw them as a small obstacle to a perfectly (now) habitable planet.

Against expectations, the Barrayarans repelled the invaders and through that war clawed their way back into the space-age with Cetagandan technology and resources. They then set about establishing an empire encompassing the rest of the habitable planets nearby and securing their wormhole against further invasions.

This expansion brought the rest of the galaxy down on them as they were seen as a warmongering race (and low-key terrifying since they beat the Cetagandans in open warfare, something the rest of the human races were terrified of ever attempting).

The expansion war ends when the Barrayaran emperor dies and is replaced by a child relative under the regency of Miles' father. Miles (the protagonist I spoke of) is born at this time, and the story hits its best stride as it follows him.

An assassination attempt on Miles' father (that catches his mother in the crossfire) while he is still unborn results in his body being irreparably damaged. He is born with bones that will always be brittle as the main trouble, and this causes him to grow stunted and short (though it is just a bone issue, he isn't a dwarf). Due to the period of isolation the planet had gone through, one of the most terrifying things to be blamed of is to be a 'mutant' which for reasons of survival meant immediate death to protect the gene pool.

Miles is cool. His adventures are great. The world-building is excellent. And unfortunately, due to timing, everyone will just assume he's "Space Tyrion Lannister," but I quite disagree on that.