SAME DIFFERENCE
One of the pitfalls of making a sequel to a game as comprehensive as Medieval is the prospect of making the two games' campaign maps too similar, but CA Australia is clearly doing an admirable job of avoiding a prevailing sense of déjà vu in this follow-up. Medieval's hugely expansive campaign map, which encompassed Europe, North Africa and Asia Minor, will now be even more impressive thanks to the addition of South America to Medieval 2.

Initially, these far-western lands will be hidden from you and the squares of the Atlantic Ocean will be impassable. However, later in the game, you'll be able to develop the technology to cross the ocean, discover America and battle with the Aztecs. You have to watch your back though - what the Aztecs lack in military technology they more than make up for in bravery and sheer numbers. So, while the Americas are there to be conquered, the Aztecs aren't likely to welcome unwanted visitors.
Well that explains the map and Aztecs then...