What was the cause of the American Revolution?

There was no single event that caused the American Revolution, the war resulted from many events which showed the Colonials that the British government did not respect them and wouldn't keep the promises made to them. The best example of this string of events is the Proclamation of 1763.
When the colonies were organized, they were given "charters", these were formal declarations by the King that the colony had specific boundaries and the people of that colony had the right to govern themselves.  Many of those charters stated the colony's boundaries went "from sea to sea", meaning from the Atlantic to the Pacific Oceans — imaging Massachusetts stretching from Boston to Portland!
In 1756, the French and Indian War began; it ended in 1763, with the English winning control over French lands in North America, including some lands that English settlers lived on.  To avoid more trouble between the Indians and the colonists, the King and Parliament drew the "Line of 1763" and told the colonists they could no longer live or settle areas west of the Appalachian Mountains.  This infuriated many colonists.  They'd lived up to their promises to the King, they fought in his army, they'd paid his taxes, they'd made North America a very profitable business for the King to own.  Now, the King took the land a previous king had promised them in their charters.  When the colonists complained, the King shut down their legislatures, sent soldiers into their cities and treated them like they were too stupid to govern themselves.
They weren't stupid, they were very smart people and they were very proud to be Englishmen.  For over 10 years, they tried to get the King and Parliament to recognize that they had rights just like Englishmen in England.  In 1775, when the King's soldiers tried to steal ammunition the colonists needed to defend themselves, the colonists ran out of patience and fought back, beginning the Revolutionary War.

There were many causes of the American Revolution. One cause was the belief the colonists had that the British were trying to control them. After the French and Indian War ended, the British passed the Proclamation of 1763, which prevented the colonists from settling the land that Great Britain received from France. The British said this was done to protect the colonists, but the colonists believed the British were trying to control what they could do. The colonists also objected to the Quartering Act, which stated that the colonists had to provide housing and supplies for the British soldiers that were enforcing the Proclamation of 1763.
The colonists also objected to new tax laws. Both the Stamp Act and the Townshend Acts established new taxes the colonists had to pay. The colonists felt these taxes were unfair, because they didn’t have representatives in Parliament that could speak about and vote on these new taxes.
There was more distrust of Great Britain after the Boston Massacre. For the first time, colonial blood was shed when protesting British actions. When the British punished the colonists for the Boston Tea Party by passing the Intolerable Acts, the colonists vowed to disobey them. When fighting occurred at Lexington and Concord in April 1775, it was only a matter of time before the colonists would declare their independence from Great Britain.
https://www.ushistory.org/us/9g.asp