Why is March Madness so popular in the United States?
March Madness is an annual college basketball tournament played in March.  It consists of 68 teams that play in a single elimination tournament until a winner is determined.  There are both men's and women's tournaments, though the men's tournament has been taking place for longer, since 1939.  Interestingly, the first tournament had only 8 teams.

The tournament is popular with basketball fans and non-fans alike.  Some people enjoy the tournament because their college or university's team is participating in the tournament.  Other fans enjoy the unpredictability of the results and cheer for a team that they adopt for the tournament.  Many people enjoy rooting for an underdog; a team that is ranked lower overall but can gain a lot of attention by winning against teams ranked higher.  This is one reason it is called 'March Madness.'