Book group selection and one of the NYT Ten Best last year, this is a richly detailed study of how the world powers stumbled unintentionally into WWI.  With extraordinary detail, Clark provides the background and month by month details of how Russia, France, Germany, the Austrian-Hungary Empire, Great Britain, and Serbia, not to mention Montenegro, Italy, Bulgaria, Romania, and the Ottoman Empire collided in 1914.  The immediate trigger was the assassination in Sarajevo of the Archduke Franz Ferdinand and his wife Sophia, but the event only led to war because the Triple Entente and the Triple Alliance had already determined to use the Balkan inception strategy to fight a war that they thought was better fought now than later.  Pan Slavism, complex and contradictory decision-making apparatus, monarchs with unclear authority, colonial expansion in Africa, Asia and China, naval strength, railroads and their importance for mobilization, the decline of empires, the lack of control of ambassadors by their home governments, the impact of popular press and internal politics all contributed, but the clear lesson is that none of these nations realized the upcoming toll of this first world war and none anticipated the disappearance of the Habsburg, Ottoman, and Tsar regimes and the seeds of WWII that would be planted at the end of this war.  A stellar contribution to the ‘how’ not the ‘why’ of WWI.