An amusing alternate-history work, framed as a collection of military uniform sketches and notes from the century before.
You pick up bits and pieces of the alternate history from the notes. Though the first, the shower of hephaustium meteors that powered the original steampunk, is introduced in the introduction -- in a solemn note compared the original steampunk to what is obviously a more advanced version of that world.
Covers approximately the same Great Powers as our end of the 19th century. With some speculation about what would have happened without the shower.