What finally led to the end of slavery in the United States?

Why did great britain finally send an ambassador to the united states in 1791? a) great britain forgave the colonies for their rebellion. b) the u.s. threatened special trade restrictions on british ships. c) great britain did not want the u.s. to become allies with france. d) the u.s. would seek a closer alliance with spain if great britain did not send an ambassador.