How did the preamble of the constitution establish your government of great Britain?

Great Britain has had a long transition from monarchial rule to democracy. The Magna Carta in 1219 limited the power of the king. The English Civil War between the parliament and the king established a constitutional monarchy forcibly limiting the powers of the king. In the 1700's, Britain was a mercantilist state that expanded its empires in North America, Africa and India with colonies. Today, the royal family is more of a ceremonial figure with little to no executive power. The United States may have influenced Britain someway, but the country has for centuries before, limited the power of monarchial rule for democracy.