I have and love Ticket to Ride: Europe, and would like to try out some of the new expansion packs (Switzerland, Asia, etc... Don't really care about 1910). I was just wondering if I would have to buy the original USA game first or if the new maps would work with the Europe set. Thanks!
Either of those big boxes is fine.
Märklin is not perfectly compatible, since the train car deck is a little bit off, and Nordic Countries only has enough trains for three players. That's why those boxes are not quite compatible with the expansion maps.
No, you only need one of the base games (Europe or USA) in order to access the train car cards, scoring markers and the player carriage pieces. It doesn't matter which base game you own. For example, the rules for Heart of Africa tell you:
This game is an expansion and requires that you use the following game parts from one of the previous versions of Ticket to Ride:
A reserve of 45 Trains per player and matching Scoring Markers taken from any of the following:
- Ticket to Ride / Ticket to Ride Europe
110 Train Car Cards taken from:
- Ticket to Ride / Ticket to Ride Europe / USA 1910 expansion
You can also confirm this yourself by looking at the Games of Wonder website descriptions for each map, for example Asia. They all say the same thing:
NOT A STAND-ALONE GAME! Requires an original copy of Ticket to Ride® or Ticket to Ride® Europe to play.
Also don't forget that Ticket To Ride: Alvin & Dexter is an expansion that can work with any of the base TTR games. It expands the game in a different direction; adding a giant dinosaur and an alien who can create havoc for those trying to build to/from a certain location.