I believe the answer is: Confederation
Confederation inherently consist of different oganizations who decided to be a part of a certain alliance in order to fight for a certain things that they need/wants. In united states, confederation among states was form once in order to fight for their rights to maintain slavery.
The correct answer is the plow. When the plow was invented agriculture was made much easier which enabled people to settle around and make surplus of food. This enabled them to trade with others and increase the size of the cities and the rest is history.
I believe it’s D not sure though