Final answer:
The Boston Tea Party and the battles of Lexington and Concord were the two events that changed the relationship between the colonies and Great Britain.
Step-by-step explanation:
The two events that changed the relatively peaceful relationship between the colonies and Great Britain were the Boston Tea Party in 1773 and the battles of Lexington and Concord in 1775. The Boston Tea Party was a protest against British tax laws where American Patriots dumped a fortune in tea into Boston Harbor. This act resulted in the British closing Boston Harbor and sending troops to Boston. The battles of Lexington and Concord were the first military engagements of the American Revolution, as American militias and British troops clashed in Massachusetts.