The correct answer is - D) the development of steel tools.
This early societies managed to have complex economies because they invented and started using the steel tools. This types of tools enabled them to create more, to significantly widen the spectrum of what they can produce and the quality of it. That gave them an advantage in trade too, so their economies were prospering and over time became complex and strong economies.
This was called Salutary Neglect. They would neglect the policies that they created for the colonies so they could focus on being a major power in Europe and European politics.
