In The Halls of Montezuma strategy card play allows you to move your forces, make events happen, activate the fleet, secure control of your lines of communication, and even invade Mexico with General Scott.
The outcome is never a foregone conclusion. Victory comes from driving Mexico’s political will down to zero; but each battle’s outcome is in doubt – a few troops performing superbly can defeat many troops performing poorly. Mexico can achieve a quick sudden-death victory before the U.S. has declared war and can bring its force to bear.