What led to the separation of colonists in the late 1700s?

When talking about the lead up to the American Revolution, it is important to remember that colonists supporting independence did not make up a majority or even a plurality of all colonists. Colonists seeking independence made up less than one-third of all colonists, so the grievances of the colonists were either not sufficiently widespread or not sufficiently serious to drive the majority of colonists toward independence.
The underlying causes of the Revolution were somewhat long-running. England passed legislation, like the Molasses Act, as a means to protect the industries of British colonies. This caused economic hardships among the American colonists, though much of the hardship was avoided through smuggling and lax enforcement. However, the colonists continued to push over the Appalachian Mountains, something which England had tried to discourage. This migration led to the French and Indian Wars. This conflict forced England to take on a significant amount of debt, which it believed the colonists should be responsible for. In an attempt to raise revenue, Parliament passed the Sugar Act and, later, the Stamp Act. These put pressure on an economy in the colonies that was in a recession after the French and Indian Wars and caused unrest among the merchant class.
The merchant class worked to increase unrest more generally, leading to the Boston Tea Party. In response, England passed the Intolerable Acts, which led to military government of Massachusetts. Rather than suppressing the colonists, it enflamed philosophical concerns about self-governance. This fueled the fires under the revolutionaries and led to the revolution.