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A Great General may join another unit in the field, giving a one-time experience bonus to units in the same tile and granting the unit it attaches to access to unique promotions.
The many conflicts that arose in the colonies of the New World forged numerous Great Generals. Jose de San Martin's march over the Andes, George Washington's stealthy crossing of the Delaware River, Frontenac's complete reversal of the fortunes of New France during King William's War, such feats defined the countries which these men formed. Without their Great Generals, Chile, Argentina, Canada and the United States would likely still be the property of their mother countries.