Video game group Kabam has picked up video game studio Phoenix Age.

San Francisco-based Phoenix Age is a game studio that created Castle Age and Underworld Empire and is working on a third game.  Castle Age can be played on Facebook and on iOS systems, while Underworld Empire can be played on iOS systems. Terms of the acquisition were not disclosed.

Kabam focuses on free-to-play games, and develops Kingdoms of Camelot, a popular game series that grossed the company more than $250 million in less than four years. The company, in 2013, acquired Exploding Barrel Games Inc., following deals for Fearless Studios and Gravity Bear, Wild Shadow Studios and Balanced Worlds in 2012. 

Other game developers have been acquisitive lately, including Amazon.com Inc. (Nasdaq: AMZN), which bought gaming studio Double Helix Games LLCin February, and Nexon Co. Ltd., which announced a deal for Thingsoft, an online game development studio, in September. 

For more on Kabam, see "The Buyside: Kabam to Keep Buying Video Game Rivals."