Which of the following best explains why americans cities grew in the late 1800s?

Numerous factors were responsible for the growth of cities in the late 1800s in the United States

growth of factories

(particularly farmers- as machines were used in many farms, moved to cities to find new jobs) led to a significant increase in the population of these cities.  Chicago is one of the examples of a growing city during the late 1800.

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the world may never know

explanation: we can only guess at how our actions may be perceived in the future. doing something really big like killing lots of people, saving lots of people, affecting the lives of lots of people is a sure fire way of being remembered in historical records. we can also make a difference in the history records by being a small influence on something bigger, whether that is as a civil servant, scientist or artist.

of course you could argue that we all affect history just as tiny cogs in a   bigger machine.

if you mean how do people influence our opinions of things which have already happened, then simply by writing a book which looks at things form a different perspective and trying to convince people that this perspective is more accurate or truthful. people do it all the time i.e. richard the third was a terrible or was he? plenty would disagree, it's just that their views aren't the most widely known.n: