During the war, both sides used African Americans for military purposes; in the South as enslaved labor and in the north as wage labor and military volunteers.
C. The Southern blockade was working.
One change that would make a positive difference would be the direct election of the president through popular vote. Currently, the Electoral College votes are given through the "winner-takes-all" method, which happens when ALL of a state's Electoral College votes are given to the nominee that won a majority of the popular vote in that state. An example would be how, in the recent election, all of Arizona's Electoral College votes went to Trump because he gained the majority of the popular votes in that state. However, because the Electoral College runs on this method, it essentially ignores a large number of votes for other candidates, such as Clinton. So, if the Electoral College was abolished, the president that would be elected would be the one that got the most votes from the American people.
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The northerners didn't need slavery because their main economy is manufacturing at factories.
Because they didn't have anything to do with slavery, they viewed it with a critical eye.
The southerners had slavery because they had giant plantations to farm cash crops. The soil was futile and had a suitable climate.