This book is like a Wikipedia article on activism, and I mean that as a sincere compliment and recommendation. 

Here's what I mean. It provides a helpful framework of history, some specifics that are maybe not relevant to everyone's needs but are close enough to spark interest in new directions, and lots of sources (in this case quotes from other activists) to prompt the expansion of research. It didn't quite provide me with next steps or concrete goals beyond more reading, but it did motivate me to get out there and try harder, and I appreciate the injection of hope on environmentalism particularly.