Age of Empires III is a real-time strategy video game developed by Microsoft Corporation's Ensemble Studios and published by Microsoft Game Studios. The Mac version was ported over and developed and published by Destineer's MacSoft. The PC version was released on October 18, 2005 in North America and November 4, 2005 in Europe, while the Mac version was released on November 21, 2006 in North America and September 29, 2006 in Europe. An N-Gage version of the game developed by Glu Mobile was released on April 28, 2009. It is the third game of the Age of Empires series and the sequel to Age of Empires II: The Age of Kings. The game portrays the European colonization of the Americas, between approximately 1492 and 1876 AD. There are fourteen total civilizations to play within the game. Age of Empires III has made several innovations in the series, in particular with the addition of the "Home City", which combines real-time strategy and role-playing game features. Two expansion packs have been released: the first, Age of Empires III: The WarChiefs, was released on October 17, 2006, and introduced three Native American civilizations; the second, Age of Empires III: The Asian Dynasties, was released on October 23, 2007, and included three Asian civilizations. Age of Empires III has sold over 2 million copies as of May 2008. As well as receiving favorable reviews, it has garnered awards, including GameSpy's "Best RTS game of 2005", and was one of the best-selling games of 2005. In 2007, Age of Empires III was the seventh best-selling computer game, with over 313,000 copies sold that year.
Question: How many months after the PC version of Age of Empires III  was released was the expansion pack Age of Empires III: The WarChiefs released?
Answer: 12