The two key concepts in play were the supremacy of the Rule of Law, and the separation of governmental powers. In Medaeval times in England, The monarch made, executed, and judged violations of the law, but was not subject to it; this was the concept of Absolute Monarchy, where all political power was invested in a single individual. Over time, the elected body, in this case, Parliament, made and repealed law. However, significant in this process was the establishment of the Rule of Law, which meant no one, not even the monarch, was exempt. The aforementioned events of Magna Carta (1215) and Glorious Revolution (1688) signify in the first case the legislative power to enact and repeal law, and in the second the Rule of Law, from which no one is exempt. These two key concepts also provided the foundation for the establishment of governance in the US.
Overall, the story here is that the nobles and parliament of England gradually took more and more power away from the monarchy. The most important events in this process would be A) forcing King John to sign the Magna Carta and B) the Glorious Revolution.
What these things (and the process in general) did for the evolution of democracy is a couple of things. First, it gave the world the idea of a limited executive that had to share power with a legislature. Second, it gave the world the idea of written statements of rights that the people had and constraints on the power of government.
That's the very short answer -- the long version requires many books...
Though powerful democratic government existed in parts of India more than 2000 years ago, this form of government had become practically extinct subsequently. The roots of resurgence of Democracy and its development in the form we are familiar with today can be traced back to the events in England in early thirteenth century, involving struggle between King John of England and Barons. This struggle led to signing of Magna Carta by King John on June 15, 1215, which marks the first step towards establishment of constitutional power in England. These developments in England later became model to be followed by many other countries for establishing democratic governments.