In general, don’t bother trying to win over the New World with money or diplomacy. Instead, be as politically incorrect as possible, and send in the troops to grab as much territory as possible before the other great powers can. (Ed: not subtle, this one, but it works. Also: go for their capitals; that way …
As soon as you develop rifle technology, turn away from producing expensive cannons and instead concentrate on infantry. Ten infantry units can take out a fort as quickly as the cannons, and they’re also a lot cheaper to produce. (Ed: I must remember to try this one.)
Be careful when it comes to playing power politics. The aim of the game is to conquer half of Europe, but do not let others benefit from your work. AI players are more than willing to scoop up major powers that you have softened up or cut off from the riches of the New World.
Weaken other empires one after the other, until you are ready to make the big play and capture those last few crucial provinces.
Cheat (Balanced resources): Hold [Ctrl] and click on the globe at the new game screen, then type Pippin. The red country will begin the game with balanced resources.
The following are from Michael Rymaszewski’s Strategy Guide. This book is essential reading if you want to get the most out of Imperialism II. Also, Slap’s Imp2 site has a good tips page.
What you have, others may lack. Use the Diplomatic screen and the Deal Book to identify current and looming shortages. You can make powerful friends and turn a nice profit at the same time.
It’s a good idea to enter bids and offer even if you have no desire to trade anything. This lets you examine the current state of the market; remember that you only receive information on the supply and demand of the commodities you bid for or offer for sale.
At the higher difficulty levels, beware of pursuing trade with Minor Nations too aggressively. When another Great Power has established an embassy and signed a pact with a Minor Nation, it probably needs the resources that Minor nation supplies, and will get upset if you barge in. Monitor the state of your relations with that Power on the Diplomatic screen.
Portugal and Holland are the trading experts among the Great Powers. These two prefer peaceful assimilation to war — although they won’t hesitate to opt for conquest at the higher difficulty levels.
Workers don’t need to be healthy to acquire new skills. If you have tobacco but no sugar cane, stock up on paper, then educate your peasants into journeymen on two consecutive turns.
A Great Power with plenty of food but little in the way of industrial resources can be expected to embark on a very aggressive course. It will have enough food to support a hug army, and will use that army to acquire territory that contains all the resources it needs.
The diplomatic attitude of Minor Nations and Tribes is unaffected by the strength of your military. However, the size of your armed forces means quite a lot to other Great Powers; weaklings are held in contempt and are viewed as possible prey.
In war, use your navy to fake multiple landings. This ruse can help disperse enemy forces, luring away the defenders of provinces that you intend to attack for real. Be warned; the other Great Powers do this, too.
To assemble a fleet of ironclads without pain, continue rapidly expanding your merchant navy, building many smaller ships rather than fewer larger ones. Once you discover Advanced Iron Working, you’ll be getting a free Ironclad for every 10 merchant ships you build.
Multiplayer: Keep a low profile! It is human nature to bind together and topple the leader, so do your best to maintain the potential for power without flaunting it. If you maintain a healthy reserve of resources and population, you can churn out a powerful military force in one turn.