Castles II expands on the original by changing the interface and adding video cutscenes on the CD-based versions.
You choose to be one of five feuding lords vying for the Crown. Conquering, spying, sabotage, diplomacy, whatever it takes--as long as you keep the Pope and your people happy. You have to reach 7,000 points to petition the Pope for the throne, and then you have to maintain those points for 4-5 game months to win the game. However, your rivals will attack you as soon as the Pope declares his support, so be sure you have a strong military before applying for the Papal backing.
Castle building is more efficient and easier to deal with. You can also set up pre-made castles on file so that you can place them quickly. Battles are set in a full alternate screen with the ability to place and command each unit.
Other than some magazine reviews, it appears the Amiga version was never officially released.
In September 1993 Interplay released an enhanced version of this game for PC CD platform, which contains over 30 minutes of documentary clips from a BBC series.
The player's guide is full of historical facts and quotations.
The video files C205.QMV, C213.QMV, and C227.QMV through C233.QMV actually have nothing to do with the game. For example, C213.QMV is of two people sitting around while Castles III scrolls on a computer in the background, and C227.QMV is of a (modern) family. To view them, copy them as C220.QMV (make a backup of the original C220.QMV first) and wait for a province to revolt.