Steam in various forms had existed for a while; firstly in 2002 as a more efficient distribution engine for Counter Strike then to provide authentication and matchmaking for the HL1 multiplayer after Valve's publisher Sierra planned to turn off their servers in 2004. They offered upgrades for all old HL1 cdkeys to a steam account and then started selling their games (I think Counter Strike: Condition Zero was the first new release) through it too... which wasn't appreciated by Sierra: http://en.wikipedia.org/wiki/Valve_Corporation#Valve_vs_Vive...