This theme is based upon the Holy Roman Empire of Germany and neighboring countries.
Initially a strung-together coalition of neighboring countries, the Empire grew to power exceptionally quick and hit its climax in the late middle ages. Decades before gunpowder became evident in Europe, the Holy German Reich had grown to such strength that it commanded every other country near it with an iron hand. No other professional army could withstand the might of the German Zweilhander shock-soldiers, nor the thunderous roar of the Gothic Knights and their steeds. The empire's generals were widely renowned for their strategic prowess; many possessing the ability to stave off much more numerous enemies with only a handful of reliable troops. The Reich gave rise to extremely heavily-armored foot-soldiers, brilliant generals, and quintessential mounted knights (mentioned above), similar to the Teutonic Order's troops in vigor, blood, and armaments.
At one time, the Holy Reich dominated much of Europe, protecting it from Eastern invaders as well as some of its own notorious occupants. The Holy Roman Empire was led by a Kaiser (emperor). Many times, France and eastern nations had tried to conquer Holy Roman Empire lands, but almost always failed in their attempts. Throughout the middle ages, the Kaisers and their armies proved too courageous to be forced into defense. And more often than not, the magnificent unorthodox tactics of the Holy Empire's generals had their enemies fleeing back home before they could cause much real damage to the Empire's lands.