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).

in contrast, the biological controls are self-sustaining, inexpensive and very effective once established. biological control could be used on thousands of golf course acres, improving their biodiversity and quality as wildlife habitat. in the process, the golf industry will be shown to be leaders in an environmental stewardship program of benefit not only to the lands they manage but also to the watersheds in which they exist.

roosevelt believed that in light of the country's recent military successes, it was unnecessary to use force to achieve foreign policy goals, so long as the military could threaten force. this belief, and his strategy of “speaking softly and carrying a big stick,” shaped much of roosevelt's foreign policy.