How do you unlock Scotland in medieval 2 total war?

To unlock Scotland in Medieval 2: Total War, you need to complete the following steps:

1. Start a new campaign as the English or French faction.

2. In the first turn of the campaign, move your army to the province of Lothian.

3. Besiege and capture the city of Edinburgh.

4. Once you have captured Edinburgh, you will have successfully unlocked the Scotland faction and can now play as them in the campaign.