U.S history prior to the American separation from Great Britain

For the past few weeks, we have been focusing on the period of U.S. history prior to the American separation from Great Britain. This week we are learning about the developments that led to independence. This week, I want you to answer this question. Prior to the first shots at Lexington and Concord and the writing of the Declaration of Independence, what development is most responsible for the American Revolution, and why? In other words, if this one thing did not happen then the United States would not exist and the American colonies would still belong to the British empire. Remember, your answer must be at least 300 words long and it must be supported with at least two (2) citations from the assigned primary sources found in Chapters 1 through 5 of The American Yawp (hereafter referred to as Yawp).