What were the key causes of the American War of Independence?

There were a number of key causes of the American War for Independence that I will briefly discuss here.
Burdensome taxes: We often hear that the American Revolution was fought in response to heavy taxes levied on the colonists. Before the 1760s, the English Parliament imposed very few taxes on the colonists in America. However, after the expensive French and Indian War, the lawmakers in London felt it necessary and proper that the colonists help pay for this conflict that was fought largely to protect their lands from the French. Consequently, starting in 1764, Parliament levied a whole range of new taxes on the colonists. What particularly irked the colonists was that they had no say in the matter. Without representation in Parliament, many colonists felt that these taxes were undemocratic, hence the popular refrain, "No taxation without representation."
New laws:Throughout much of the 17th and 18th centuries, the colonists were largely left on their own to govern themselves and make their own local laws. At around the same time that the taxes discussed above were imposed, Parliament also began issuing new laws for the colonies. Once again, the colonists chaffed at having laws imposed on them by a political body in which they had no representatives. They felt that these laws were an imposition on their freedoms as independent Englishmen and Englishwomen.
Punitive responses: There were naturally a number of protests against these new laws and taxes. In 1773, After a group of dissidents in Boston destroyed several shipments of tea in protest of a tea tax, the British government responded harshly by instituting what was known as the Intolerable Acts. The port of Boston was closed, the charter of Massachusetts was revoked, the local administration of justice was hampered, and British soldiers were quartered in private homes. This greatly worried many colonists who saw these actions as tyrannical and a threat to their livelihoods.
A spirit of independence: As you can see, the above topics were infringements on the independence of the colonists. It is important to remember that most English colonists in the Americas at the time of the Revolution were the descendants of people who left England to live in a land where they had the freedom to live according to their own beliefs and wishes. This independent spirit lived on, and when the English government began throwing its weight around, many saw this as a violation of their natural rights.
Additionally, the Declaration of Independence explicitly states the reasons why the colonies rebelled against Great Britain in its list of grievances. This is a great primary source to study as you can read the actual, specific complaints that led to the War of Independence.
http://www.let.rug.nl/usa/essays/before-1800/was-the-american-revolution-a-revolution/background-history-and-the-beginning-of-the-revolution.php