The main goal of the game is to become emperor of Europe. However, you are free to do whatever you wish. There is no set time limit whatsoever. There are two ways to eventually accomplish the goal. The first is to conquer everything from Dublin to Antioch. This can be done completely by military power, but there are many other paths to go by, such as inheriting land because you married one of your princesses to the prince whose father died. However, given the fact that it is very hard to watch after an empire as it grows, the player can simply "Claim the Title" if he thinks he's powerful enough to become emperor of Europe. This means that the player will be voted for or against other major powers in Medieval Europe to become the supreme king of Europe. However, if your proposal is shot down rather fast, every major power will declare war on you for attempting to take the Supreme Throne. There is, every certain amount of time, a game induced vote for the throne of Europe, and it is possible to win this without any votes if you own enough provinces, as you vote yourself to the post. Note that it is difficult to seize the throne by war, first one must destroy all the competing kingdoms. View their military power and attack the one with the lowest first, slowly building enough power to kill the final enemy. A more peaceful method of victory involves acquiring all the Kingdom Advantages. To get all of them requires several coastal villages to bring in Rare Goods and subsequently a large kingdom.
There are certain kingdoms which may also expand by conquering and reuniting the core provinces of a larger empire. If you are playing as Kiev, Muscovy, (also Kazan) for example, capturing the provinces of central Russia (Polotsk, Muscovy, Ryazan, Smolensk, Kiev, Chernigov, Novogorod, Tver, Voronezh, Saratov, Vladimir, Kazan) allows you to reunite the empire of Russia. Likewise, Normandy may establish the kingdom of England by capturing the key provinces of Britain (and also destroying the kingdoms of Wessex, York and East Anglia). Once the conditions for forming a new nation have been met you may choose whether or not to change the name of your kingdom; if you do so, your empire receives a one-off gold bonus, as well as receiving a number of bonus provinces. For certain kingdoms, this can offer a very quick way to expand. The flip side, of course, is that neighbouring kingdoms may unite their own nations, and some of the bonus provinces they receive may be territories that are taken away from your kingdom.