As the title suggests, Ferguson sees common causes fueling and linking the disruptions of the 20th century. Thus for him, the "war of the world" begins with the Japanese defeat of the Russian navy in 1905 and doesn't end until the conclusion of the Korean War in 1953.

Seen this way, World War I and II become peaks in a series of eruptions around the globe, all fueled by the incendiary confluence of three developments.

The first factor was economic. The 20th century was marked by rapid changes in prices and growth rates, and such volatility -- whether in the direction of boom or bust -- triggered social and political instability.

The second development was social: Ethnic tensions, already growing, were heightened by the century's economic ups and downs.

And the third factor was the decline of traditional empires. With their powers waning, Russia, China, Austria-Hungary and the Ottoman Empire lost control over their ethnically mixed borderlands -- the very areas where so much of the century's violence started, including World War I.

The weakness of the old empires also tempted rising states such as Japan, Italy and Germany.

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