"A Brief History of Manga" by Helen McCarthy is a wee, hardback, glossy book. It gives a pretty good overview of manga, starting from about 700AD! Okay, that bit's really, really brief. Two pages along, I discovered that some British people published newspapers in Japan during the 1860s, which included cartoons.
Most of the book is about manga in the 20th century, linking some of the manga developments to periods of history. I really liked the little timelines along the bottom of each page, and the colour pictures showing the different manga mentioned in the text. I also enjoyed seeing how the drawing styles changed as time went on. I've got some ideas for manga to try now too!
McCarthy has written other books, and one of them is in my classroom (the Hayao Miyazaki book). She's a good writer and doesn't make things too complicated.