Professional Armies (Civ3)/The Middle Ages/Civilopedia

Professional armies are armies made up of people who know how to do nothing but fight. Thus, for them to be maintained, they had to be 
constantly paid. The only person in most medieval kingdoms able to afford this was the king, and aristocrats were understandably uncomfortable 
about the prospect of the king having a large, experienced, well-armed military force answerable only to himself at his constant disposal.
In many ways, though, the rise of professional armies was the nobles' own fault. Classic feudalism typically extended to a lord the right to 
levy his vassals' citizens to man his armies; this obligation was unconditional and had no time limit. Vassal lords did not like this, and worked to 
promote a much more limited arrangement in which serfs could only be obliged to serve in the army for forty days. But forty days was hardly enough time 
to train unschooled peasants into soldiers, and therefore rulers opted not to bother, instead taxing their vassals for money to pay full-time soldiers. The 
result was an overall increase in royal power throughout Europe, as the idea caught on and kings saw armies made up of professional soldiers defeat civilian armies 
many times larger in size.