There are, to date, three books in Graydon Saunders' Commonweal universe. They are not a trilogy, though they involve overlapping sets of characters in more or less linear timeflow -- so it's a series. The March North, A Succession of Bad Days, and Safely You Deliver are available on Google and Kobo and probably Smashwords as DRM-free ebooks. Minor spoilers for details and word usage follow -- not plot.
There is magic, and Saunders takes it seriously: somewhere about 150,000 years or so of magic has completely overturned the geography, geology and ecology of the planet. In the Bad Old Days -- everything prior to about 500 years ago, and everything outside of the Commonweal since -- patterns repeat. A person discovers they have magical Talent and either kills themself learning about it or kills a bunch of friends and family accidentally. They seize power, set themselves up as a magical dictator, and then fall to any of the obvious perils: trying to conquer a land with a stronger magical dictator; experiments in immortality gone awry; or, of course, rebellion.
Somewhere during their rise or consolidation these jerks tend to try to build supersoldiers, slave workers, purpose-bred animals and/or magically-enhanced plants. As soon as the creation ends, evolution takes over... Weeding is a dangerous occupation.
The Commonweal has managed about 500 years now through a lot of luck followed by hard work. The luck centered around the discovery of a magical ritual called a focus, in which a bunch of low-level magic users -- almost anyone, really -- come together to temporarily pool their magic. Of great import: they must all truly be willing to work together. Of equally great import: they are stronger together than their additive sum.
The hard work that followed involved the establishment of laws centering around enforced equality -- none shall gain more than ten times any other -- and an absolute ban on magicians as rulers. The peace is enforced by the Shape of Peace, a magical construct that embodies the Commonweal's constitution, and The Line, the professional core of an otherwise volunteer military force. The Line is highly regulated and completely forbidden from conquering -- defense only.
By all means, start reading with The March North, which tells the tale of The Line's detection of and defense against an invading army, and then learn more about civilian life in the next two books. But be warned: Saunders likes packing several meanings into a sentence, and the characters' tendency to use ungendered pronouns is highly significant -- gendered pronouns do exist, but they always indicate a special interest.
Good stories, great characters, amazingly well-thought-out setting. I recommend them.