I've always found the immediate aftermath of WWI to be fascinating, both in the way it doesn't match what they taught us in school, and how it loops back to events as far back as the 1700s that set things up. As 38OVI recommended, A Shattered Peace discusses how many of these events set up the world for WWII, and events down to today and beyond--ever wonder why Putin is so convinced the US/NATO are out to destroy Russia? Look to the 1918-1920 intervention by Wilson/Churchill/Masatake.
No English-language scholar has really gotten into the events in Eastern Europe the way Glantz has for Soviet involvement in WWII. Siberia To-day is a good intro to some of the internal politics the interventionists were dealing with in the Russian Revolution. Fighting the Bolsheviks and Quartered in Hell: The Story of the American North Russia Expeditionary Force 1918–1919 are good. The History of the American Expedition Fighting the Bolsheviki is available online on Project Gutenberg, as is With the "Die-Hards" in Siberia (from a British perspective); both are worth a look. The Way of the Heavenly Sword: The Japanese Army in the 1920's get into both the Siberian Intervention and the evolution of the Meijaa military to the Imperial Japanese Army.
And if you've really got time to get into the underlying world politics, there's always Churchill's The World Crisis, 3,000+ pages covering the real start of the war in 1911 through the post-war events up to 1920, including the Treaty of Versailles. This one was, and still is, somewhat controversial. More than one scholar described it as Churchill's autobiography; Churchill himself said it was not a history, but should be taken with other accounts (so it was his, or his view of the British perspective, on the events 1911-1920). Great book either way (actually, great books, as it is 6 volumes!).