Multiple reasons. Firstly, Britain (a world-wide power) was setting humongous taxes on imported and exported goods. (As in the 'Tea Party' the Americans rebelled by throwing the tea into the sea). The colonies were irritated by this whole control, and wanted more power and say in what taxes were put on them.
"<span>B. Its labor system remained undisturbed" is very much not true. Almost the entire labor system of the South depended on slavery, which was abolished during the war. </span>
<span>Albany Plan. The Albany Plan of Union was a plan to create a unified government for the Thirteen Colonies, suggested by Benjamin Franklin, then a senior leader (age 45) and a delegate from Pennsylvania, at the Albany Congress on July 10, 1754 in Albany, New York.</span>
To quote the witch in Snow White "Who's the fittest of them all?" Who but those who think they are powerful enough to occupy colonies who supply raw materials to be shaped into manufactured articles, to be sold back to the colonies?
That is the definition of imperialism. It is the colonization by force of those unable to prevent the colonization. Imperialism is the creation of an empire by colonizing people that can't prevent their own subjugation.
Does that not sound like survival of the fittest to you?