There are at least two ways to answer this question.
On the one hand, we can say that the war was brought about because of the British government’s attempts to tax the colonies more and to exert greater control over them. After the French and Indian War, the British government attempted to do both of these things. The British wanted more tax money from the colonies to help pay for the costs of the war (which was a war that had benefited the colonists). They wanted to exert more control to make sure that the taxes would not be evaded. These actions angered the colonists who had become accustomed to being able to run their own affairs. This divergence between the colonists’ desire for autonomy and the British desire for control led to the war.
On the other hand, we can say that the war was the result of natural processes. The American colonies had grown to the point where they would inevitably have wanted independence regardless of what happened. They had become economically powerful. They had come to have a large population. They were far from the “mother country” and understandably felt that they were ready to be independent. In short, the colonies simply “grew up” and became too old to still be controlled by their “parents.”
Either of these can be seen as the major cause of the war.