The Somerset decision was in 1772 just three years before the war started. Trouble was brewing for almost ten years before that as the Stamp Act was passed in 1765. The British did not ban the slave trade until 1807. Britain did not end slavery through out the empire until 1833. William Wilberforce did not enter Parliament until 1780. The Committee for the Abolition of the Slave Trade was not formed until 1787.
And cotton was in no way the basis of wealth on either side of the Atlantic in 1770. Cotton production in England was 10% that of wool in 1770. The production of cotton as a major staple did not occur until the development of the cotton gin. If the author can’t get this right...
But it’s their ‘truths’ that are important—not facts.