I used to play Age of Empires III on my PC, a lot. It was pretty much my favorite PC game with the possible exception of Heroes of Might and Magic. I had some ideas for a campaign based on the rise of the Ottomans, where the player would, of course, play the Turks. I even finished the first scenario and started on the second one.
Then I ran out of time and interest. I am certain I will never return to this project, but I wanted to publish the outline because I thought it was a good idea for an historical campaign.
The campaign covers the period of history from the mid-14th to the mid-15th centuries during which the Ottoman dynasty rose to prominence in Asia Minor, surrounding and swallowing up the decaying remnants of the Byzantine empire. There is also a diversion in the story line, in which the Turkish forces must contend with the threat of the Mongols under Tamerlane.
The Ottoman dynasty gets its name from Sultan Osman I, who declared himself independent from the kingdom of Seljuk Turks. His base of power was in Anatolia, centered around Ankara (then known as Angora), the capital of modern Turkey. There were many Ottoman rulers during the century or so that the campaign covers, but in the campaign story line the player will assume the role of a long-lived Sultan, and then that of his equally long-lived son. Neither will be named, emphasizing that they are fictitious characters.
The campaign is broken up into six scenarios as follows.
The Turkish fleet is bombarding the city of Gallipoli, currently in Byzantine hands. The young prince of the Ottomans must lead a daring mission to land a detachment on the coast, locate a group of siege engines, and then use them to assault the city and destroy the towers that are holding off the Turkish fleet.
I was actually able to build this scenario, using the programming rules to have the player move a starting force to a location where some battering rams would come under the player's control. The victory condition was destroying a castle behind a wall, and the rams were needed to complete this goal. But one had to be careful not to lose one's starting force to stray engagements, because they were needed to marshall and defend the rams.
It worked out pretty well, though it took a lot of time to playtest. I needed to find the right balance between the attacking and defending forces.
In this scenario, the player actually must build up a settlement and muster the units to assault Adrianople, again in Byzantine hands. Since the computer player is also making units, one must be defensive at first. This was supposed to simulate a drawn out military campaign to siege and capture a city.
I started working on this scenario but did not get very far. The rest of the scenarios are ideas only.
By now, the player has assumed the Ottoman throne. The scenario simulates the famous Battle of Kosovo in which the Serbs were defeated on the Plain of Blackbirds. The Serb forces would be represented by the Goths, probably. An interesting twist is that some of the Serbs betrayed their brethren and fought for the Turks. Presumably, the scenario would be set up such that the player would have to make contact with the Serb allies in order to have enough forces to win.
Nicopolis was the Christian crusaders' last stand in the Holy Land. In this scenario, French and Teuton forces are defending a city which the Turks must capture. An effort by enemy cavalry to end the siege must be countered by the player's own cavalry force.
This is where the story takes a turn; the Mongols have taken Angora! The Sultan must stop his campaigning to rescue his capital. It would probably be a timed scenario, the goal being to kill Tamerlane within the allotted time.
At this point, the player is the son of the previous Sultan, about to achieve the crowning glory of the Ottoman empire and live up to his father's legacy. A huge battle to conquer the last Byzantine city ensues.
This page by Steve Barrera 2009-2013