What caused the start of slavery?? (make it a written answer about 3 paragraphs.)

Newspaper started by john campbell:

How has the elimination of trade barriers affected the movement of goods among member countries of the european union? a. member countries are able to produce all the goods they need. b. goods can move freely among member countries. c. member countries no longer need to trade with countries outside the eu. d. larger countries are able to import more goods than smaller ones.

What words in the preamble to the constitution reflect the principle of popular sovereignty