1936: Political systems gain and hold on to power by exterminating great masses of people. Soviet Russia begins purges that kill eight to ten million citizens in two years. Nazi Germany kills nearly as many during the Holocaust. A million die during the Spanish Civil War.

Today: International peace-keeping forces from the United Nations often intercede in abusive regimes.

1936: Hitler's secret police force, the Gestapo, takes over the regular German police force to spy on citizens more easily.

1986: West Germany and East Germany are still divided, with East Germany aligned with the Soviet Union.

Today: Having been reunited in 1990 as the Soviet Union collapsed, the Federal Republic of Germany is one of the most influential European nations.

1936: The Great Depression that has affected the United States through much of the 1930s is just as devastating to the rest of the world, leading people to support...