Hey guys, just thought I'd put up some suggestions for the Scotland faction (I study history at the University of Glasgow, Scotland)
The Braveheart image of Medieval Scotland is almost totally wrong - Scotland was in fact a prosperous kingdom, if smaller than some. All you have to do is take a look at some of the spectacular castles, mansions, monasteries, abbeys, churches etc. to see that the country was far from impoverished. While Scotland did develop a unique clan system, by the time of Medieval 2 Total War the Scottish army had adapted European modes and equipment of fighting.
Infantry: the Celts may have invented chainmail, and early Scottish infantry would have worn mail armour with jackets and other standard western European armour. Spears were the most popular weapon, but halberds/long axes, lochaber axes, short axes, swords, blunt weapons and knives were also used, often with shields. The majority of units would be a levvy from the common folk of town and countryside but also included some of the more well-to-do and nobles. Armour was made at home or imported from the Continent - and France often supplied Scotland with weapons and armour as part of the Auld Alliance agreement.
In later ages, partial plate and full plate replaced mail and leather, with the nobles being especially well armed. Spears were replaced with longer pikes and larger two-handed swords to cut through enemy armour. At the advent of firearms, armour slowly became obsolete. It is at this time which we see highland dress definitely appear on the battlefield, with different colour/pattern tartans being worn by highlanders along with more typical European uniforms being used by Lowlanders at least until the start of the 18th Century. Scottish armies were not too slow to adopt firearms; at first using pike-and-shot with artillery support until modernisation left gunners as the main military profession.
Cavalry: Early records show Viking reports of the Scots using heavy cavalry in battle. Scotland was indeed capable of producing heavy cavalry throughout the medieval period, although of much lesser numbers than England and France. Light cavalry was given a scouting, flanking and harassing role, as well as famously scattering the English archers at the Battle of Bannockburn 1314. Scottish cavalry armour would have followed West European conventions. The Border Reivers were particularly famous and deadly, operating on both sides of the Scotland-England border for loot, and who also worked as mercenaries. Scotland did indeed have knights, although as the vanilla game states, nobles often preferred to fight on foot. Also used were hobilars; infantry who travelled to the battle on horseback.
Archers/Gunners: Scotland, like England and France, used shortbows, longbows and crossbows. France often imported Scottish longbowmen to fight in the constant wars against England, and the England-based Osprey history books attest there is no reason to suppose Scottish archers never used the longbow. Archers would also have used armour typical for each time period. There were, however, less of them and were less experienced than those of some other countries - although some were of very high quality, the Scots Guard of France and the archers from Ettrick and Galloway for instance. There is also no reason to suppose that later-era Scottish gunners or artillery were technically inferiour to other factions, in fact some are highly credited (find out about Mons Meg, a great cannon still at Edinburgh castle which was cast in Flanders!).
In summary; tartan and highland dress would have been seen to a limited degree in earlier medieval Scottish armies, armies which the majority of the time would have appeared much like other European armies. Archers and artillery were very capable, as were late era gunners. A heavy emphasis was always placed on anti-cavalry infantry, however, and the Scottish army was never as large or power as some of its neighbours. Scotland was, however, able to fight deep into England and English-occupied Ireland and Isle of Man, go on Crusade and provide large armies to its Continental allies. The navy was not neglected and often played important roles.
By the time firearms were being widely adopted, highland dress appeared on the battlefield on many Scottish soldiers, often used with pikes, halberds and great two-handed swords as well as muskets and pistols. In later times the two-handed claymore sword was replaced by a lighter one-handed sword and targe, a small shield embossed with Celtic designs.
Scotland was not half-barbaric, but was mostly developed and had a strong army, economy and a relatively advanced government system which allowed it to withstand over a millenium of foreign invasion and maintain its independence.
Hope this has been interesting and helpful Good luck with the mod guys, and I hope everyone is enjoying the summer Oh, and I'm really looking forward to playing the mod!
Pax;
-Steven
Addendum: I hope Flanders is kept as a faction from the earlier previews, the region was nigh-on independent and very important. I vote for that, anyway!