Since which year have the FEI World Equestrian Games (championships for equestrianism) been held?

The FEI World Equestrian Games are the major international championships for equestrianism, and are administered by the Fédération Equestre Internationale (FEI). The games have been held every four years, halfway between sets of consecutive Summer Olympic Games, since 1990. Prior to that year, all ten of the FEI's individual disciplines held separate championships, usually in separate countries. The modern WEG runs over two weeks and, like the Olympics, the location rotates to different parts of the world. Riders and horses competing at WEG go through a rigorous selection process, and each participating country sends teams that have distinguished themselves through competition as the nation's best in each respective discipline. At the 2010 Games, 57 countries were represented by 800 people and their horses.