For anyone with several days to kill I recommend The War of the World by Niall Ferguson. Don\'t be deceived by the initially intimidating length, fondness for graphs and tables of economic growth. This is a heavyweight but accessible trawl through the \'100 years of hatred\' that was the Twentieth Century.
Challenging the conventional wisdom that the Second World War began in 1939, Ferguson hammers home exactly how much hatred, violence and mayhem was unleashed over our recent past, from the scientific atrocities of the Nazi regime to the random acts of violence committed by every side. Backed by statistics on every conceivable aspect - including which Allied army you should surrender to as a Wehrmacht soldier - horrifying first hand accounts and a strong argument, this is sometimes not comfortable reading but it explains the horrifying events of our last century in a global, economic and political context that made sobering sense to me.