The answer is: Lincoln claimed to defend the Union and attempted to convince the South that the secession was illegal and impossible.
Lincoln gained massive popularity on the northern states because he advocated for the establishment of slavery, and the south was threatening secession because they relied heavily on slavery as the major workforce that sustain their economy.
Lincoln realized that if the southern states manage to secede from united states, The republican party would receive the largest amount of blame for the separation, and their chance to free the slaves in southern states were gone. Because of this, he swore an oath to defend the union and prevent the south from seceding in his inaugural address.
Vietnam war revolve simple belief by America that communism was threatening to expand south-east Asia Korea war the spread of communism during the Cold War
The unprecedented levels of production in domestic manufacturing and commercial agriculture during this period greatly strengthened the USA economy and reduced dependence on imports. Capitalism is greatly efficient and allowes Large economic growth!
