In a general sense, it was because of the oppression that Britain had put over the colonies that led to the Declaration of Independence. Some of the many factors included tax impositions, the Boston Massacre, Coercive Acts, and Common Sense by Thomas Paine.
Moreover, the declaration was written by a committee of five including Thomas Jefferson (primary author), John Adams, Benjamin Franklin, Roger Sherman, and Robert Livingston and ratified on July 4, 1776 in Philadelphia.
