What caused a "shift in public opinion"

In the three weeks since George Floyd’s death, public opinion on race and policing has zoomed left. Support for Black Lives Matter is skyrocketing. Almost 60 percent of Americans think police are more likely to use excessive force on an African American suspect than a white suspect — a sea change from 2016, when only 34 percent of registered voters said the same. And an overwhelming majority of Americans now say they support a wide variety of police reforms, even if polling suggests that “defend the police” is still a radioactive slogan.

Explanation: Credits: The Washington Post; Public opinion on policing has shifted.

the expansions of railways meant manufacturers could ship goods easily.

the building of the railroads changed the environment of the west.