The rebellion against Great Britain became a revolution as American radicalism led to poorly thought-out reaction from the British government. This happened in part because the American colonies had “outgrown” their status and because the British government did not want to lose its authority.
Acts of rebellion or resistance like the protests over the Stamp Act do not necessarily lead to revolutions. In the case of the American colonies, though, they did. When the Americans rebelled, the British government cracked down on them, perhaps harder than it needed to. When the British cracked down, the Americans became more radicalized. They turned to greater acts of defiance, notably the massive destruction of property that we call the Boston Tea Party. They became more incendiary in their denunciations of Britain and calls for independence. This led to even more repressive responses from Britain.
All this happened in part because the American colonies no longer needed to be colonies. The colonies had become more populous and more prosperous than before. They were certainly wealthy and large enough to form their own country. They had been used to governing themselves to a great degree during the time of “salutary neglect.” These factors helped make the Americans less willing to accept British crackdowns. At the same time, the British government feared looking weak and losing its authority. It felt that the colonies were an important part of the British Empire and needed to be kept. It felt that backing down would make this harder to accomplish. For these reasons, the American rebellion ended up as a full-blown war for independence.