Just finished
July 1914: Countdown to War by Sean McMeekin
Fantastic breakdown of the month or so between the assassination of Archduke Ferdinand and the first roll out of troops for war. It details the numerous "WTF are you kidding me?" moments of diplomatic incompetence, geopolitical posturing by skilled diplomats, and basically destroys the notion that Kaiser Wilhlem II was a warmonger who marched Europe into war.
Churchill called the month leading up to World War I the greatest drama story ever told, this book breaks it down with access to resources we simply didn't have until recently (mainly with Russian interests).
This story needs to be a miniseries on Netflix or HBO.
https://www.amazon.com/July-1914-Countdown-Sean-McMeekin/dp/0465060749
It put me on such a World War I-era binge that I'm onto
The Campaign of the Marne by Sewell Tyng, though I'm worried it's dated since it came out in 1935.