What was the main purpose of a castle

Two gymnastics teams are intense rivals. the first team has started recruiting new gymnasts from different cities and even foreign countires in an effort to build a stronger team. after learning this, the secondteam begins its own recruitment campaign to find better gymnasts. over a period of months, each team recruits dozens of players, each time trying to find a better recruit than its rivals most recent addition. which idea from the cold war is most similar to this scenario