I am surprised that so many Americans think the US invented all this. The US political system is an evolution of English culture and those same values have evolved in parallel in all western countries.
The limitation of government power was a widespread concept in medieval Europe. It was much later that Kings began to assert more absolute powers and the experiment ended when the King was killed (that oughta teach him).
Remember medieval Kings were considered “primus inter pares”, first among equals and in many cases were elected. Their powers were severely limited, not only by custom but by the practical fact that they depended on the nobles for everything. They had very little real power. Their powers to tax were also very restricted.
BTW, that link to a new European Constitution is very interesting. I had no idea they were about to adopt a constitution.