1) The first successful mass-produced personal computer, the IBM PC, was introduced in 1981 and played a significant role in popularizing the use of computers in homes and offices.

2) The Danube River, flowing through ten countries in Central and Eastern Europe, is the second-longest river in Europe. It has played a significant role in the cultural and economic development of the regions it traverses and is a popular waterway for river cruises.

3) The Treaty of Tordesillas, signed in 1494, divided the newly discovered lands outside of Europe between Spain and Portugal, leading to the colonization of the Americas.

4) The FIFA World Cup is the most-watched sporting event globally, with billions of viewers tuning in for the tournament held every four years.