Why did Britain become the earliest democratic constitutional country in the world?

In the middle and late Middle Ages, in order to dispel the power of the church and feudal lords and increase his own financial resources, the king began to foster and win over the civic class, encouraging commercial activities and urban autonomy. With the development and prosperity of commercial activities, the former political enemies of the king-the church and the lords-slowly disintegrated. The king finally achieved dictatorship, a sly rabbit died and a running dog cooked. In order to collect money, the king began to attack his former ally, the upstart businessman. But at this time, Dajia, a wealthy businessman developed by the citizens, was full of feathers. The king wants to raise taxes, but the businessman doesn't. So the war began. Unexpectedly, the merchants were not only rich, but also strong in fighting capacity, and the king was defeated. So the king had to compromise and make a constitutional monarchy.