Age of Empires III Walkthrough

2.3.2  Hold the Fort

Primary Objectives:
-Survive until Cooper's men arrive.
-Destroy all the Mexican Army's Town Centers

Secondary Objectives:
-Upgrade both Trade Routes to Trains. (300 XP)

Your first objective is to defend the fort.  Pull your Musketeers into the
fort. Set the cannons in your fort to Bombard Mode.  There are two Trading 
Posts sitting on two Trade Routes running through your fort.  Set the Posts to 
collect whatever resources you need.  Research Iron Horse in both Trade Posts. 
With your cards, send for artillery.  Have Amelia Black, one of your hero 
units, exit the fort and build Trade Posts at open sites, denoted by large 
white circles.  Each Trading Post site has an Outpost (thankfully, yours) 
guarding it.  Have one research Frontier Outpost and Fortified Outpost.  Build 
artillery and distribute them at corners, with a bias toward the longer sides 
of your fort.  Build a few skirmishers.

Defending your base from the waves of enemy troops is simple.  When your fort 
is attacked, have the artillery closest to the enemy bombard the largest clumps
of soldiers, and have your skirmishers pick off individual soldiers (having 
your artillery bombard lone soldiers is wasteful of opportunity).

Be sure to keep Amelia walking around the map building Trade Posts.  Do not
forget to set your Trade Posts to collect the resources you need.

After the timer runs down, Major Cooper's reinforcements will arrive.  You will
receive around twenty units of calvary, fifty Skirmishers, and eight Howitzers.
Your new objective will be destroy the enemy Town Centers.  As usual, have your
artillery bombard the buildings from afar while you keep your soldiers nearby 
to defend the artillery.

Methodically work your way through the towns.