: Crusaders, Saracens, and Byzantines all wrapped up into one super-theme that would include Crusader Castles, Constantinople, and the various Saracen factions and their buildings. One could break it down into yearly sub-themes: Crusaders, Saracens, then Byzantines. Fleets would have to be addressed, too. This theme could last a decade if LEGO approached it with a more dedicated Playmobil mentality. The obvious drawback is the religion vs. religion theme that LEGO would probably want to dodge (which is why breaking it down into seperate Crusader, Saracen, and Byzantine themes might be more palatable).
Merry Olde England
: Robin Hood, Nottingham, Shirewood. More emphasis on village life. Earlier simplier castles. I could have made a specific "Medieval Village" theme suggestion, but this would essentially cover it in a more marketable format.
War of the Roses
: Full plate in all it's last styles, cannons, handgonnes, full courtly pagentry, rich merchants, and the last gasp of castles before they lost their tall walls and fortifications changed forever.
: Charlemagne and his Paladins, Saxons, Arthur & Post-Romano Britons, Vikings...oh hey, this one is almost under way....
: Teutonic Knights (had to work them in), Black Forest, and things general with a more Germanic bent. Toss in Austrians and Swiss and get the middle europe alpine construction look.
In regards to previous comments: The building style for the Hundred Years War would be burnt timber (it was more about destruction than construction
). I won't suggest Romans or Greeks, because they are essentially from pre-Castles era.
Bricklord: You should accumulate these suggestions and THEN post the poll once you have a good cross-section.