King James I believed that Kings were "accountable to none but God only", he his subjects had no right to speak about how they wanted to be governed.
James argued that "The state of monarchy is the supremest thing upon earth; for kings are not only God's lieutenants upon earth, and sit upon God's throne, but even by God himself are called gods ... Kings are justly called gods, for that they exercise a manner or resemblance of divine power upon earth: for if you will consider the attributes to God, you shall see how they agree in the person of a king."
As an aside, I don't think that God calls anyone God, that is idolatry. Anyway, at the time, the public did not agree with James and his son Charles was executed on Tuesday January 30th, 1649!
Charles attempted to dismantle the rights of the people and of the parliament, and after a civil war was executed by Richard Brandon, an executioner more used to common criminals. In the place of that we had a 'Lord Protector', Oliver Cromwell.
When he died, Britain was at a bit of a loss of what to do now. So they sent for the dead King's son, Charles II, who was in exile. Charles II then killed all the dissenters and the monarchy was restored.
Things could have been very different, we could have become a democratic republic. Did we made a mistake? Of course, whichever way you decide, in the twenty-first century we do not need to execute people to reform the political system.