The 3rd post lists some of the main reasons, and I totally agree with the 5th post that gives reference to France's recognition of the colonies. In addition to their financial support, France's naval and ground support provided during the final year were major contributions to the American victory.
One essential factor was the support of France. The assistance of the French was absolutely key in the victory by the Americans. The French support provided the American forces with generals who knew the enemy British very well. French aid helped to pay the costs of the Revolution. General Lafayette was one of General Washington's strongest allies and advisors.
Are not the majority of these points largely relevant in a number of conflicts throughout history? These factors certainly crop up again and again when we examine a wide variety of wars and other nations' foreign policy commitments. #2 is also correct however in identifying foreign aid as another vital factor that contributed to victory.
You can compare many of the reasons the British eventually let the colonies go with the reasons why the United States got out of Vietnam:
1) Distance - supply lines were thousands of miles long and expensive to maintain
2) Cost over time in blood and treasure
3) Colonists' knowledge of the terrain
4) Motivation of a volunteer army fighting for independence vs. a draftee army fighting to make it home again
5) George Washington, Nathaniel Greene and Henry Knox - effective colonial Generals - British ones were hard to come by
6) Colonies could play defense - all the revolutionaries had to do was survive, British had to conquer and pacify
7) Support of a significant part of the local population
I am certain that you would be able to find many different reasons as to why the Americans won in the Revolutionary War. I think that any standard US History book could indicate this. I would propose that I sense that the knowledge of American geography helped to create an absolute realm of victory for American troops. American soldiers fully understood their terrain better than the British did. Leaders like Nathanael Greene and Francis "the Swamp Fox" Marion were skilled at being able to understand specific tactics matching specific situations better than the British did. Additionally, strong leadership from Washington and other commanders helped to crystallize purpose and focus in action. Finally, I would say that help from overseas was vitally important to American success. Contributions from the French and the Spanish, amongst other nations, were critically important to the victory against the British, ensuring that control of economic and political control would rest with the Americans.