Edward Johnston’s famous manual, Writing, Illumination & Lettering has been scanned by the Internet Archive and made available on their website. The introduction talks about the evolution of western calligraphy, a discussion that ties into Myrna’s historical review.
Searching their site for “calligraphy” turns up loads of references, not just in western style calligraphy. Some are available online but others provide information for obtaining a physical copy. To see the online versions, look for the icon of an open book in a circle.
You could spend hours checking out these books online.