Answer:
Urbanization
Explanation: Millions poured into cities for jobs in factories during the industrial era. This rapid urbanization resulted in overpopulation, crowded tenements, strain on city service, health issues etc.
1. sectionalism was the main cause of the civil war. the southern states seceded from the Union because they didn't want President Lincoln to free their slaves.
2. The Southern was devasted because it couldn't its agriculture products to the North or overseas. The Northen economy thrived on its manufacturing
3. the bureau provided assistance to tens of thousands of former slaves and impoverished whites in the Southern States
The argument of missile defense in the nation of Cuba is a non-starter because the USA will never willingly allow a nation that is so close to its territory, and is an ally of its arch enemy, Russia, to have such a defensive system installed, because it will also mean that Russia may use Cuba as its military base and threaten the USA territory at any moment, from close proximity, and also they will have a protection by any attack as a response.
The president is Donald trump
Realpolitik.
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It's a theory where politics are based on practical matters rather than theory/ethics.