Empire Building Board Game

Hmm, games of that type can become too bloated and it is a challenge to keep the rules as simple as possible while retaining depth.

I'd suggest you don't strive for overt historical accuracy or too many elements. Imo, ideally, you should find a simple, at least somewhat original and distinctive basic mechanic and let your game grow from that.

Also, try thinking outside of the box... The knee jerk reaction is to have some kind of a board with distinct regions or hexes which contain resources and then you place units and buildings on top of it. Roll the dice to resolve battles, have some resources gathered etc. There has been literally thousands of games like that and making your game stick out would be difficult indeed...

For empire building done a bit different.. Say, there is Domain (not Domaine) aka Lowenhertz where, for example, you play action cards to extend your borders. So it is the border pieces that are crucial rather than the territories themselves. It's a very "german" take on the theme. Or purely card-based Citadels.

Or maybe try to combine two mechanics which are not new but in a novel way? Say, carcassone-like simple expansion and exploration but with citadels-like building cardgame? Remove fighting from the map completely, make it card-based (say like in Cosmic Encounter) and you'll have a much simpler and less cumbersome design... It depends on whether your emphasis is on building or fighting.. or both?

However, if you are going for a full-blown strategic wargame with all the trappings, I'd suggest you pay extra attention to the length of each players turn and whether other players can interract during it. Imo, "Ticket to Ride" has a brilliant way of solving it with every player being permitted just one action per turn - it's similar to what you have in mind as well as Puerto Rico but much simpler and faster.

Yeah, I remember Game of Thrones now... (the first one :) - played it only once. As I recall it had basically a Cosmic Encounter-style combat resolution. I really like that mechanic but when you combine it with postional play it might become just a tad bit too complex... (unless you're going for complexity, of course :) Look up CE if you haven't played it yet, it's an old but goldie classic and you wouldn't believe how many editions, variants and add-ons it has been through. It's really a gold mine of game design ideas... Btw Richard Garfield mentioned it as the prime inspiration for Magic the Gathering, so you really can't get a better endorsement than that. Also Knizia's LotR Confrontation has pretty much what you described so you might want to look into how it's done there.

Btw I just played Saga again, a little known german gem with a very interesting central mechanic.. It's a german wargame (O.o) played with cards numbered 1-4 in 6 colors. There are 6 castles and each turn you play just one card out of your hand (it's a bit more complex, but this 's the gist of it). The color of the first card you play determines to which castle your army is heading and you cannot change it later. The cards in following turns can either add to the existing army strength (they must be of different color) or you can start another army going somewhere else. Once you have more in your attacking army then the force defending the castle, you take it over and place your attacking army into it. So, its basically a bidding game and the players watch each others armies creeping towards their castles... without any board at all! It's quite an elegant mechanic and maybe it can be combined with something else.. hmmm..