Many years ago, during the formative days of this nation, crews manning the sailing ships that brought the people and goods here suffered smallpox in great numbers. No one knew what caused this plague.
American Indians were trading goods for anything, including land. The blankets from infected ships were used as trade also. Indians then were infected with what was an unknown diease in this country, smallpox.
It wasn't done deliberately, it was done through pure ignorance of science and the origins of any diease.
Since Indians had no resistance to smallpox, many died.
I believe it refers to the fact that Mr. Trent, who founded Trenton, NJ and Mr. Amherst, who founded Amherst, Massachusetts, were the instigators of putting smallpox spores into the blankets given to the Indians, killing many thousands of them.