One of the main ways in which the U.S. Constitution reflects the principle of democracy is that "It creates a republic government, which is the same as democracy," since people are represented by officials and legislatures in Congress.
One of the key causes of the Civil Wars was how people wanted slaves to live. Northern America didn't want slaves, and wanted them to be free. However, the Southern half disagreed with this, as they used slaves very commonly. Another would be trade. Northern America was heavy in industry, and wanted to build the stuff they needed, whereas Southern America traded crops with Britain to get their supplies. Hope this can help! :)
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Oliver Hazard Perry,I believe.