Numerous things had led to the fighting between the colonists and Great Britain in 1775, which was the start of the Revolutionary War. The first shots were fired in Lexington and Concord, which kicked off the war.
The colonists and Great Britain had high tensions for a long time, they did not agree, and the colonists wanted independence from Great Britain. Before the French and Indian War, Great Britain had practiced salutary neglect with the colonies. This meant that they essentially left them alone and let them do their own thing. After the war, this changed.
The French and Indian War was very expensive and Great Britain needed a way to pay for it. They were also providing troops to protect the colonies after the war, which was fought on the soil of the colonists. Because of all this, Great Britain thought it was fair to tax the colonists in order to pay off some of their war debt. The colonists did not agree with this though, as they had nobody to represent them in the British Parliament, known as "taxation without representation."
While a lot of the tensions rose from the colonists being taxed, other things had bothered the colonists like the Quartering Act and the Intolerable Acts. Not just "one" thing had led to the fighting between the colonists and Great Britain, though unfair taxing is known to be the main component.