Adiamante by L. E. Modesitt, Jr.

Long ago on a future Earth, the three human factions nearly destroyed themselves and their world with war. The cybs (short for cyborgs) were expelled from earth. Now they are back in ships with adamantium hulls and a chip on their shoulders. Adamantium an almost indestructible material, expensive to produce and usually ecosystem-destroying to do so. That doesn't matter to the cybs, and never did. But now they have these ships and are poised to wreak havoc on old Earth.

But those that remained on Earth have a very different society and ecosystem than the one that the cybs left behind. All uses of power or privilege require a personal act of contrition to society. All things must be done so that they do not have lasting or harmful effects on the ecosystem that has survived past conflicts. The cybs believe that Earth society has fallen from its power and will be an easy conquest from behind their impenetrable hulls. But are they seeing everything?

Mr. Modesitt has long questioned the uses of power and force in his novels, and the subsequent reactions to that use of force. In this one, he puts forth a possible solution to the ever-escalating uses of force, although in the end, the answer is the same. While not the most engaging of Mr. Modesitt's stories, it makes some very interesting suggestions as to how society should address those uses of the power it commands, and the specific responsibilities of those who are in charge of that society and that usage of its powers.

I maybe a bit off the mainstream, but my favorite science fictions are those that address social, economic and political issues at their core. This book is the epitome of just such a book. Set in the far future and with technologies so far beyond present day as to find them almost incomprehensible, this book is still essentially about people and their almost over-whelming need to force their belief system on others. The solutions aren't perfect, even to  the people in the story, but they have that most effective way of lasting; they work.