In the Declaration of Independence, the Revolution is framed as a revolt against tyranny. In it, government is understood as contractual in nature, having been originally created for the purpose of safeguarding natural rights. The revolutionaries accused Britain of having broken that contract, acting as an oppressive force where the colonies were concerned. On these grounds, they argued, revolution was a morally justified action.
Moving beyond the realm of argumentation and discourse, you must understand that the American Revolution emerged out of a very gradual escalation of tensions which unfolded over years. It was ultimately shaped out of the transformations which came about from the French and Indian War (itself part of a much larger, global struggle known as the Seven Years' War), which had only ended in 1763.
The experience of the Seven Years' War had left Britain facing severe financial strain. This led it to become far more interventionist within colonial matters than it had been before. Traditionally, the British government had granted the colonies a great deal of autonomy, largely on pragmatic grounds, given the sheer distances in communications between Britain and America.
However, in the aftermath of the Seven Years' War, Britain began to impose new taxation schemes and to more rigorously enforce mercantile law. Additionally, the British government passed the Proclamation of 1763, that barred settlement west of the Appalachians (an act that caused great discontent among the colonists).
The colonists responded to these new taxation measures by organizing. They sought to apply pressure on the British government through the use of boycotts. Meanwhile, more radical groups such as the Sons of Liberty employed violence to achieve their ends. In 1768, responding to these growing tensions, British troops were sent into Boston. This action further strained an already fragile situation (as seen by 1770's Boston Massacre).
What we see here is a picture of gradual deterioration as once strong ties between the Colonies and Britain became increasingly frayed. Responding to the Boston Tea Party of 1773, the British government would pass a series of acts to punish the colony of Boston, condemned throughout the colonies as the Intolerable Acts. These punitive actions rallied colonial support against Britain and led to the first Continental Congress in 1774. The Battles of Lexington and Concord would be fought in 1775, while Common Sense and the Declaration of Independence would both be published in 1776.