Right, in Empire Total War and Napoleon for that matter, there are two types of strategies, one smart, one stupid.
The stubid one is to go directly to a long war with the nation/s you want to conquer where you risk beeng destroyed by enemy ambushes or you manage to conquer them all.
A more smart and safe but still fun way to conquer is to wait and fill up your armies, put them on the border or next to the city/ies you want to conquer, then when the right moment comes, YOU LAUNCH A FULL SCALE ASSULT ON THE NATION/S AND TRY TO CONQUER YOUR TARGET/S. Then, no matter if youÂ´re succesful or not, you make peace as fast as you can and then you do this over and over again untill you conquer the world. The only consequense is that every one will turn hostile to you because of "Dishonored Treaties".