This is one of the best histories of what the west was like in the years leading up to WWI, possibly Tuchman's finest work. (Certainly taken in tandem with The Guns of August, which is a virtual continuation of Tower.)
Tuchman focuses much of her narrative on pivotal figures and events to bring that focus down to a specific and human level. The recounting of the Dreyfuss Affair, for example, is frighteningly relevant. A must-read.