Dota 2 is developed and published by Valve Corp. This game is the sequel to Defense of the Ancients, which was a mod created for Blizzard Entertainment Warcraft 3. The development of this game began in 2009 and was officially released on Window, OS X and Linux based systems. It has been criticized in the past for having a steep learning curve and game play complexity. It is the first game ever to use the source 2 game engine. Dota 2 has been widespread in the esports industry with players competing in many tournaments throughout the world. They Dota 2 tournaments have some of the highest dollar amount prize pools of any game throughout the world. The largest event is held in Seattle in the Key Arena and is known as the international.