1910s: Vladimir Ilyich Ulyanov, known to his supporters by the name Lenin, leads the Russian revolution, overthrowing the czar and instituting a dictatorship of the proletariat—or common people—led by himself. Over the next several years Lenin works to build the Communist Party into an organization that can effect worldwide revolution, and tries to get all separate communist parties to commit to the Soviet cause.

Today: Many formerly communist countries, including the former Soviet Union, currently employ democratic systems of government.

1910s: During World War I, in an effort to rally support at home, various countries on both sides rely on printed propaganda and other methods of psychological warfare that demonize their enemy.

Today: After an attack on the World Trade Center in New York City and on the Pentagon in Washington, D.C., that leads to war in Afghanistan, Hollywood capitalizes on...