Can anybody recommend a comprehensive textbook on military hardware that would include not only American but French, German etc arms too?
Back in the day, we always used to rely upon Jane's Guides on Ships, Aircraft, etc. These books are comprehensive analyses of military (and some civilian) hardware around the world.
They often contained information on the derivation of different pieces of hardware too and other interesting facts.
Unfortunately, the site will charge you for access to the Guides, however, a good library might have copies (or a subscription) to the site.