A, the black plague. This is because the mongols would invade and actually use people infected with the plague to throw over walls of towns to infect the people inside.
It's the Navigation Acts. The Navigation Act was passed on 9 October 1651 by the Rump Parliament drove by Oliver Cromwell. It approved the Commonwealth to control exchange inside the states. It fortified a long-standing guideline of government strategy that English exchange ought to be conveyed in English vessels.
