I'll take a crack at Modding, but others may want to expand on it.

>>>>>>>>>>>>>>>>>>>>>>>

MODDABILITY

IMO, MTW was VERY easy to mod. I'm not very skilled at this stuff, but I can handle Notepad and Excel, which is really all you needed to change almost everything in the game (the exceptions being graphical stuff like maps, skins, models, etc.)

As I said above, the single-player campaign could be started in one of three time periods (or 4 if you had Viking Invasion). Each of these time periods had a massive .txt file associated with it. In each period's .txt file, you could easily change things like:

The kind of maps used when province x was invaded from province y
The buildings each province started that period with
The units each province started that period with
The base farm income value of each province
The trade goods in a province
Which factions were playable
Whether a province is susceptible to floods, earthquakes, etc.
Whether one could walk an army from one province to another (so like whether there was a "land bridge" between Granada and Moracco, or between Wessex and Flanders)
You could easily create and add new factions, pick their religion, etc.

Then there was another massive .txt file that held all the raw combat data for each unit in the game. I found it easiest to edit this one with Excel. Anyway, you could easily change attack values, defense values, morale, number of men in the unit, how likely that unit was to be spawned with a Hero, which factions could build that unit, whether any factions got a cost discount when building that unit, etc. Many of the modding problems people have had with RTW units (changing movement speed, killing speed, etc.) were super easy to change in MTW. CA says this is because the RTW data was hardcoded with the 3D animations. I have Dawn of War, which also has 3D units, and I know you can easily mod melee damage and movement speed in that game, so I think it's a bad excuse. Relic even provided their modding tools to make modding even easier. Anyway, there were two other .txt files that controlled all the features of buildings and of missiles (like how longbowmen's arrows flew, trajectory, stuff like that). So, early on in RTW, there was a big problem with missile units shooting into the backs of their own commrades and killing them. If MTW ever had that problem, you could easily have modded it out by adjusting the trajectory of the missiles.

In short, MTW was extremely easy to mod. There was hardly any aspect of the game you could not easily change just with Notepad or Excel.

>>>>>>>>>>>>>>>>>>>>>

Someone want to give a description of the general time period, some historical background, and/or describe the strategic situation/style of some of the major factions? Some that immediately come to mind are:

England

France

Germany

Spain

Italy

Byzantium

The Turks