Of the 56 men who signed the Declaration of Independence, 26 were lawyers. The American Revolution was not fought over the issue of paying taxes. It was fought in part over a question of law, that being who had the authority to impose taxes - Britain or the colonial government.
To colonial leaders, taxation without representation was one of the major causes of the American Revolution. Restriction of free trade and restriction of free speech were also very important considerations.
The words "United States" are not in the Declaration. Those words were not used until the Continental Congress wrote the Article of Confederation.