The correct answer among all the other choice is D. U.S. naval blockade of Cuba. This event resulted in the greatest threat of nuclear war. Thank you for posting your question. I hope this answer helped you. Let me know if you need more help.
Industries made alot of pollution so the air was full of smoke and working conditions inside factories were harsh. Health risking conditions.
Demand for employment let to child labor and exploitation of women and men working for the company. They worked on hours for little pay.
Cities started getting crowded since people were having urban areas, looking for jobs in the cities which caused overpopulation issues.
I don’t believe that the Spanish caste system was fair because they separated the population into the categories that they believed were fit. So the lowest of them were Africans. Europeans and Peninsulares were put onto a pedestal and made to be seen as the more higher-ups. The way they categorized them by their intelligence and color of their skin was harsh. The whole system was rigged to benefit the Europeans and not the Natives and Africans which is why I see it as unfair and not right.