What was the major issue between the North and the South starting in the 1850s?
A. industry
B. cotton
C. slavery
D. women's rights

The answer is slavery.

Here is cited proof:

The article "The American Civil War" by ReadWorks illustrates, "The major issue between  the North and the South was slavery. Starting in the 1850s, Northerners became more and  more hostile to the idea of slavery on moral grounds, while slavery continued to be an  accepted fact of life in the South."(1).

a

explanation:

the  equal rights amendment  (era) states: "equality  of  rights  under the law shall not be denied or abridged by the united states or by any state on account of sex." congress first introduced the era in 1923, but the campaign for ratification took off in the 1960s during the  civil rightsmovement.