The Barbarossa Campaign
"Age of Empires 2" has five individual campaigns. "The Wallace Learning Campaign" is basically a tutorial that will teach you the basics to get through the rest of the campaigns. "Part One: An Unlikely Messiah" follows the story of Joan of Arc. "Part Two: An Arabian Knight" is about Saladin, the leader of the Saracens, and his siege on Jerusalem, Jihad and Richard the Lionheart. "Part Three: Crucible" tells the story of Genghis Khan and the Mongols. "Part Four: Holy Roman Emperor" is about the life and death of Frederick Barbarossa, his supposed ally, Henry the Lion and Barbarossa's attempt to reign over the Pope.
The Barbarossa campaign is ultimately the most difficult campaign of the four, mainly because it takes place in the more advanced Castle and Imperial Ages. The campaign begins with the unification of Germany and then moves into Barbarossa's invasion of Italy before ending with the Crusade to the Holy Land. Henry the Lion, a powerful German prince, first makes his appearance just after the unification of Germany. Although Henry swears allegiance to Barbarossa, he spends most of his time while Barbarossa is in Italy building bigger castles, leading more troops and influencing more people than Barbarossa himself. Betrayal is a part of the AEO Barbarossa campaign, and trusted allies can turn very quickly. That is why Barbarossa decides to put Henry the Lion to a test to determine whether he really is an ally.
Henry the Lion Skirmish
In the Barbarossa campaign, your military units will consist mainly of Teutonic Knights, Men-at-Arms and battering rams. The Teutonic Knight is powerful but slow, and is easily taken down by archers or converted by monks.
When the scene begins, start building as many battering rams as you have resources for. Find Henry the Lion's castle and position half of your men and battering rams around it. They will be needed later in the story.
Move the rest of the men to the northern part of the village and destroy the Polish castle that is situated there. Try to move the troops in on the castle from the west to avoid the archers in the watchtowers. As soon as the castle is destroyed, Henry the Lion will change his stance from Ally to Enemy. The minute that happens, use the troops that you stationed by his castle earlier in the game to destroy it.
While the troops are destroying Henry the Lion's castle, build more rams, Teutonic Knights and Men-at-Arms. Be sure to destroy Henry the Lion's military buildings--watchtowers, barracks and stables--once the castle is destroyed. This will disable Henry the Lion and allow you to complete the campaign.
At this point, return to the west village and release the villagers and then continue destroying any remaining troops and buildings. Poland will eventually resign.