The American Revolution involved the British and the American colonists. One of the catalysts was how the British Parliament was treating the colonists.

The changes that had taken place in the mindset of the colonists were a part of what caused the American Revolution, but were not the sole cause.
The events that occurred over the prior 40 years of abuse by the British Parliament were the other factors that finally led to the revolution. During the 40 years of British rule, colonists were required to put up with a large degree of taxation. The colonists were concerned with the fact that they apparently had no say over how they were governed and believed that the corruption of the rich and powerful in English society would infect their new form of liberty.
Before the revolution, the American colonists constructed a thriving life here in America and were thousands of miles away from the presence of England’s King. The majority of colonists lived outside urban centers. The degree of urbanization in the colonies was very low.
Work was plentiful and available to all that needed it. This led to a very low poverty rate among the colonies. There was also religious freedom practiced in the colonies as there had never been in England.
In the colonies, there was no titled aristocracy. This brought citizens into relationships and made men equal to one another. Living in America thus changed the colonist’s view of freedom and independence. In England, generally only the privileged and aristocratic people owned land.
Owning land was much more common among the colonists. More than 80 percent of white men owned property and were allowed to vote in elections. This meant that men in America could vote and have a say in their governing body.
The colonists had elected a legislature in each of the states with the responsibility to govern the state and pass laws concerning the rule of order.
These changes in the mindset of the colonists made them distinctly different from the beliefs of the general English citizen. The independence that the colonists enjoyed made them aware of the fact that their life in the American colonies was very different from life in Europe.
The colonies had very poor response to the rule of the British troops before the revolution. They had developed a very strong allegiance to the colonial laws and enforcement of those laws. The issue of slavery was still very much alive in the colonies. This gave the colonists a direct appreciation of how important freedom and self-governance was in their lives.
England passed numerous taxes, all of which were catalysts for revolution. The acts passed by the Parliament included the Molasses Tax, Sugar Tax, Stamp Tax and the Quartering Act. Each of these was aimed at asserting British rule in a stronger way.
Stiff taxes were applied to goods imported from the West Indies including, molasses, sugar and rum. Various items imported from England would carry high taxes such as coffee, tea and textiles. A Tax Stamp was then required to accompany all public documents including newspapers and legal documents.
These new taxes were designed to pay the salary of troops and governors of the British crown and to help pay for the war debt of the Seven Year's War. The British Parliament felt the colonists should help pay for the war expenses incurred by Britain. The final straw was the Quartering Act that required the colonies to house and provide for the stationing of 10,000 regular troops in colonial towns.
In 1775, the colonies elected delegates to the First Continental Congress to pass the Articles of Confederation. This was not sufficient to rule the American colonies but it did place the complaints before the British Crown.
One year later, the Second Continental Congress was held and the Declaration of Independence was written. This outlined exactly the abuses and complaints of the colonists and declared their formal intentions to become an Independent Country no longer under the rule of Britain.
So, why did the American Revolution happen? It was because of 40 years of power abuse and the changes that took place in the colonists as a result of living in the American colonies.