Proactive and makes me reflect. It will take some more time and research. But I would say that Massachusetts was a colony under the King. It wasn’t as though Massachusetts started slavery but the King’s colony started the slave trade. There was little choice as a colony since it belonged to the King. The corporations making the trades were in England and could only trade under receiving permission from the King. No one in any colony could get a license with permission at that time.
The first slaves under the British Crown arrived in 1619 after being kidnapped from traders by the British merchants. So it’s more correct to say the King allowed the corporation to trade slaves and reparative the profits back to England, Liverpool, Manchester. The decision and permission could only be granted by the King. The colonies were only extensions of Britain and not free territory for another 126 years or so. The colony of Massachusetts resisted the Crown better than Virginia or South Carolina, primarily because of Puritanical resistance towards the Monarch who they hated.
Their “Southern” staunch beliefs in coming to America were to escape his reign and work towards their freedom based on their individual effort. Slaves were anathema to that individuality but imposed. The colonists in Virginia or South Carolina didn’t come for “fanatical” beliefs, but with aristocratic pretensions and ambitions for social climbing through wealth imposition. Thus, slaves didn’t conflict with their ideals but amplified their ambitions. Their wealth and status aspirations were based on their profit maximization for their corporate owner. The more cash crops were sent back to England with the balance sheets that included the worth of slaves—their assets and production value and depreciation—the greater the chance of achieving status and financial recognition in the King’s inner circle. They did come to America to revolt against the King but to work for the King, in tandem of supporting his authoritarian reign.
Southern values were markedly different from the New England ones, in stark opposition to them even. This is why we see Massachusetts abolishing slavery in 1783 in a court decision and the South resisting it up until the war broke out. These were two nations, divisible, with lived ideals that were—and still are—in direct opposition. “We” were never united, but the politicians keep saying this (until at least the gaslighting wears off).