and became important trade centers in the Mediterranean

What would lead a historian to consider two events to have a relationship of correlation rather than causation?

Although the three-fifths compromise northern and southern states reach an agreement that allowed for ratification of the constitution, in the long run it had a negative effect on the nation because a) it gave too much power to the executive branch of the government. b) it forced the founding fathers to add the bill of rights to the constitution. c) it was only a temporary solution to the argument between "free" and "slave" states. d) it gave too much power to state governments and not enough to the federal government.

Why was the treaty of versailles harsh on germany?