Question: What tournament is annually held in Las Vegas since the 1970s?
Context: The USA Sevens (also sometimes referred to as the Las Vegas Sevens) is a rugby sevens tournament held annually during the second weekend of February in Las Vegas in the United States.  The USA Sevens is the largest annual rugby competition in North America, drawing over 60,000 fans, and is broadcast live in the United States by NBC and NBC Sports.  The USA Sevens was introduced in 2004, and has been held at its current home, Sam Boyd Stadium in Las Vegas every February since 2010.  The USA Sevens tournament features 16 teams representing countries from every continent, including the host, the U.S. national team. The World Series of Poker Europe (WSOPE) is the first expansion effort of World Series of Poker-branded poker tournaments outside the United States.  Since 1970, participants had to travel to Las Vegas if they wanted to compete in the World Series of Poker (WSOP).  Although the WSOP held circuit events in other locations, the main tournaments, which awarded bracelets to the winners, were exclusively held in Las Vegas.  The inaugural WSOPE, held in 2007, marked the first time that a WSOP bracelet was awarded outside of Las Vegas.  From its inception to the 2013 tournament, players from 19 countries — USA (10), France (4), UK (3), Denmark (3), Canada (2), Norway (2), Portugal (2), Italy (2), Afghanistan, Germany, Indonesia, Spain, New Zealand, Sweden, Tunisia, Switzerland, Australia, Italy and Finland — have won bracelets. The World Series of Beer Pong (WSOBP) is the largest Beer pong tournament in the world in number of participants and cash prizes offered.  It has been held close to or in Las Vegas since January, 2006. "Lakewood" Louie is an American poker player best known for his success at the World Series of Poker (WSOP) in the late 1970s and early 1980s. Robertson High School (RHS) is a public senior high school in Las Vegas, New Mexico.  The school is part of the Las Vegas City Schools District in former East Las Vegas.  The building dates from about 1945, when it was known as Las Vegas High School.  The school was renamed Las Vegas Robertson High School in 1958, after the old Las Vegas High School burned down and a new building was constructed.  W. J. Robertson had been the Superintendent of the Las Vegas City Schools since 1941 when he suffered a fatal heart attack on November 26, 1956 at the age of 55.  Mr. Robertson, born in Kansas on November 3, 1901 also served as Principal at Las Vegas High School for many years prior.  The colors of RHS are red and white, their mascot is the Cardinal.  The enrollment currently stands at 607. The Las Vegas Invitational is an 8 team college basketball tournament held during Thanksgiving of NCAA Division I men's basketball season annually since 2003.  The Tournament was held at Valley High School in Las Vegas, The event used to be sponsored by Findlay Toyota, until moving to the current site the Orleans Arena in 2006.  From 2006 to 2013 the sponsor of the tournament was IBN Sports.  Continental Tire is the current sponsor of the tournament. The Trofeul Popeci was a tournament for professional female tennis players played on outdoor clay courts.  The event was classified as a $50,000+H ITF Women's Circuit tournament.  It was annually held in Craiova, Romania, from 2007 to 2013.  From 2007 until 2010 the tournament was classified as a $10,000 event on the ITF calendar.  The last edition of the tournament was in 2013. The World Series of Poker (WSOP) is a series of poker tournaments held annually in Las Vegas and, since 2005, sponsored by Caesars Entertainment Corporation (known as Harrah's Entertainment until 2010).  It dates its origins to 1970, when Benny Binion invited seven of the best-known poker players to the Horseshoe Casino for a single tournament, with a set start and stop time, and a winner determined by a secret ballot of the seven players. Carolina Moraes (born 5 April 1980) is a former synchronized swimmer from Brazil.  She competed in the women's duet competition with her twin sister, Isabela Moraes, at both the 2000 and 2004 Summer Olympics .  Both also competed for Ohio State University, winning 11 national championships, including the team routine title in 2000, and four straight titles in duet and trio routines between 1999 and 2002.  Following the Olympics, Carolina and Isabela retired and joined Cirque du Soleil, with their first performance being as part of the 2005 World Aquatics Championships opening ceremony.  Both have been part of the cast of "Le Rêve", a show presented in Las Vegas since 2007, though Carolina is less frequent as she travels with her husband, part of Cirque du Soleil's technical team. Joe Schoenmann (born in Madison, Wisconsin) is an American journalist and nonfiction author who has lived in Las Vegas since 1997.
Answer: World Series of Poker