Analysis of information sources in references of the Wikipedia article "Professionalism in association football" in English language version.
the game is complex enough not to be invented independently by many preliterate cultures and yet simple enough to become the world's most popular team sport
During the twentieth century, soccer emerged as the world's most popular team sport
Soccer is the most popular sport in the world and is an industry worth over US$400 billion world wide. 80% of this is generated in Europe, though its popularity is growing in the United States. It has been estimated that there were 22 million soccer players in the world in the early 1980s, and that number is increasing. In the United States soccer is now a major sport at both the high school and college levels
