Counter-Strike has been played as an eSport since the first version of CS came out. Clans were founded and the teams started to play matches and scrimmages against each other.
But much have happened to eSports in general since CS 1.6 and when Counter-Strike: Global Offensive came out it was very natural that the events and tournaments around the world boosted the prize money as the interest had expanded a lot.
Unfortunately Counter-Strike have fallen behind a bit on the prize-pools lately compared to eSports like Dota 2 and League of Legends. Still, some players have collected impressive cumulative amounts to this date.
One interesting fact to notice it that a lot of the top10 are Swedes. It is amazing that one small nation can perform so well in a game that is played by so many people around the world
Prize-money collected by top 10 Counter-Strike: Global Offensive Players