Zynga confirmed tonight that SoftBank will invest $150 million in the social game company. Zynga will also open a joint venture withSoftBank in Japan to develop and distribute social games across Japan. We reported the long-awaited deal would happen earlier this week.

The new venture will be called Zynga Japan and it will focus on enabling social games anytime, anywhere. That means that Zynga’s games such as FarmVille are likely to make their way to social mobile networks in Japan, where SoftBank Mobile is one of the leading mobile carriers, and on the PC as well.

The joint venture will extend Zynga’s reach to a wider global audience and help it diversify away from Facebook, which accounts for the lion’s share of Zynga’s revenues. The announcement is timed to SoftBanks’ latest earnings call today. Masayoshi Son, chairman and chief executive of SoftBank, said in a statement, Zynga is a leader in social games and I am delighted to partner with them to introduce their social games to Japan. We share the same vision as Zynga in social games and look forward to working together to create a social game powerhouse.”

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Mark Pincus voiced similar sentiments about expanding into the Japanese market and gaining insights from it. Japan is a strategic market because  its social mobile game market is growing fast and it can teach Zynga lessons about the future of mobile in the U.S.

With the money from SoftBank, Zynga will have an impressive war chest. It has raised around $520 million in funding to date, including an unannounced $100-million plus investment with Google, which plans to use Zynga games in a new Google social network that will challenge Facebook.

One things is clear. Social gaming is no longer in its infancy. It has become a market of giants.