The UFC has brought fighters from three other major promotions into its fold over the years: PRIDE, the WEC and Strikeforce. Zuffa LLC, then owner of the UFC, purchased PRIDE in 2007. In 2010, the WEC merged into the UFC, giving the promotion lighter-weight fighters on the roster. And Zuffa purchased Strikeforce in 2011.
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Daily Debate: Which UFC purchase was most valuable? Strikeforce, WEC or PRIDE? – MMA Junkie