By forming various organizations.
The European Union, for example, unites Europe (Minus Britain these days) under one banner, thus preventing fighting.
A more direct example is the North Atlantic Treaty Organization. NATO protects the "North Atlantic" and Europe from terrorists and invading countries by using the combined military strength of multiple nations.
South Carolina was the first state to secede from the Union on December 20, 1860. It was called southern nationalism. Other states began to secede, however, no state had the right to secede but the federal government didn't have the power to stop them.
The answer is C because america cut taxes known as Tariffs because if they cut taxes they could put more price on over sea shipping so that trade stays within the united states instead of helping other country's <span />