Paris 1919 - what the post-WWI peace negotiations were and why they failed;
The War That Ended Peace - her take on why the war started. Not as detailed in events as Clark's The Sleepwalkers but better on the people involved.
If you are into WWI I just finished watching the Week-by-Week Episodes of “The Great War” on YouTube. Outstanding series.
The Sleepwalkers is very good! I was shocked to read that there was a serious worry that the British military would stage a coup due passage of the Irish Home Rule Act. Some viewed that a war on the continent would give the military something to do other than seethe about that act.