I think this is the correct answer, but let me know if it is incorrect. People were having more children per family.
An informal deal was struck to resolve the dispute: the Compromise of 1877, which awarded all 20 electoral votes to Hayes; in return for the Democrats' acquiescence to Hayes' election, the Republicans agreed to withdraw federal troops from the South, ending Reconstruction.
The Soviets were setting up nuclear missiles in Cuba. This meant that they were now able in theory to launch a nuclear missile directly at large parts of the USA and it was therefore viewed as a threat by the USA. I hope that helps.
