What was the condition of the American colonies at the time of the Declaration of Independence?

At the time of the American Revolutionary War, the 13 original British/American colonies were fairly prosperous. The American colonies had provided Great Britain with a strong foothold in North America below its possession of British Canada. The American colonies, if not overtaxed and basically taken for granted by Great Britain, might have made the British Empire even stronger than it already was. There is nothing that would have prevented Great Britain from remaining to this day the most powerful nation in the world. This is of course subject to debate.