The 3DS is still not even a year old and already it has sold over 4 million units in the United States alone.

It was not long ago that Nintendo revealed the 3DS had surpassed first-year sales of the original DS, selling over 2.37 million units as of the beginning of December. We know 795,000 3DS units were sold in November, and it seems December was another big sales month for Nintendo's newest handheld gaming system, though we won't get NPD sales figures until later next week.

Nintendo notes the 3DS has now sold more in its first nine months than Wii did in that same stretch. Life-to-date sales through June 2007, as reported by the company at the time, were 3.81 million in the U.S., and the Wii still had another month or two to go before it was available for "nine months," so it's unclear exactly how 3DS outsold it over that span of itme. Regardless, that's not a completely fair comparison as there was a shortage of Wii systems for an extended period of time following its launch, a shortage which some felt was orchestrated.

The 3DS recently surpassed the 4 million units mark in Japan as well. It was available a month earlier in Japan (launching on February 26, as opposed to North America getting it on March 25) but might not have made it to that mark were it not for Japan's strong interest in Monster Hunter; the Circle Pad Pro-supporting Monster Hunter 3G has helped to spur sales of the system in Nintendo's home country since the game was announced.

Keep in mind Nintendo expected a total of 4 million units to be sold by March 31, 2011 worldwide, a figure it wouldn't reach until later in the year.

Today's announcement mentions that Super Mario 3D Land and Mario Kart 7 are the first 3DS games to reach 1 million units each in the U.S. That's true in the U.S., though worldwide it's The Legend of Zelda: Ocarina of Time 3D that was the system's first million-unit seller.

The strong sales of 3DS in recent months can be largely attributed to both the holiday shopping season, and perhaps even more importantly, the $80 price drop. After initially struggling out of the gate and contributing to Nintendo's first annual loss in 30 years, a price drop was announced in late July. In the U.S. it went from costing $249.99 to $169.99.

Those who purchased a system before the price drop went into effect on August 12 have received 20 free games -- 10 NES games and 10 GBA games, the latter of which Nintendo has no plans to sell to the public. The NES games will eventually be made available on the eShop. In Japan, some have already begun to show up.

For the entirety of 2011, Nintendo says it sold over 4.5 million Wii units and 3.4 million DS units in the U.S. to go along with the 4 million 3DS units. The Wii's install base is now up to 39 million and the DS' has passed 51 million.