1950s: Chairman Mao Zedong rules as Communist dictator in the People's Republic of China.

1980s: Chinese students in Beijing's Tiananmen Square stage a pro-democracy demonstration. Hundreds are killed when the Chinese government suppresses the protesters with tear gas, rifle fire, and tanks—which crush protesters.

Today: China is the only remaining Communist major power in the world.

1950s: Fifteen-year-old American, Bobby Fischer, becomes the world's youngest chess player ever to attain the rank of grand master, making chess history.

1980s: After two decades of programming computers to play chess, Deep Thought, a computer designed to play chess at the level of the grand masters, is created. At the same time, HiTech, a computer developed at Carnegie Mellon University, defeats a human grand master for the first time.

Today: Deep Blue, Deep Thought's successor, defeats Russian Garry Kasparov, world chess champion, in one of...