What is the monroe doctrine and how has it impacted the americas in the 20th century?

In hand stitched dreams which clue tells you that the historical period of the events will be important in the story

In ohio in 1872, the cleveland massacre was a)a violent labor dispute at standard oil refineries in cleveland. b)a takeover by standard oil of the refineries in cleveland. c)an attempt to stop standard oil from becoming a monopoly. d)a failed attempt by standard oil to take over other refineries.

Who did the first work in creating vaccines