The following procedure involves editing a game file so it is advised that you create a backup copy of the file before proceeding. Go to the 'medieval ii total war\data\world\maps\campaign\imperial_campaign' directory and find the 'descr_strat' file. Then using a text editor program cut and Paste the 'unlockable' section into the 'playable' section and save the file. Launch the game and every faction will be available. You can also unlock the Papal Estates, but not the Mongols, Timurids or The Aztecs.
Type in rogan,madras,istanbul,george,vindaloo or houston for some cool units to crush opposition but delete the units when you have finished because they are expensive.these cheats make the game crash in the battle screen so they can only be used in the overall screen.
First hit the @ button near enter to bring up the console. Then type in: Create_unit "City/character name" "Unit type" 1-5(this is for the number of units) 1-9(this is experience) 1-3(this is weapons upgrade) 1-3(this is armour upgrade) E.g. Create_unit "london" "Templar Knights" 4 7 3 3 (include the speech marks) Then, in London you will have 4 units of Templar Knights, with 7 experience, full armour and full weapons upgrade. I swear this cheat works, but you MUST remember the speech marks.