Your goal is to take control of one of the countries involved in the conflict in order to come out on the winning side of the war. Of course, depending on which country you select, the conditions for winning will differ. That is to say, while if you control the French army you have to conquer almost all of Europe without letting any invading army cross your border, if you control Turkey you have very different goals.
Just like with all of the other grand strategy games, you have to stay on top of all of the details that relate to your own country as well as everything around it. This means that not only will you have to lead and supply your armies, but that you will also have to make sure that your country is good enough to give your soldiers something to fight for.
March of the Eagles is an excellent strategy game. Though it's based on somewhat out-of-date technology and the graphics are not great, it will entertain you for longer than a game usually does. If you take advantage of the impressive multi-player mode, which supports up to 32 players online, you will enjoy it even more.
The demo only allows you play part of the campaign.