Answer:
It is hard to give only one cause to such a big historical event. The decay of empires can be a long duration event with a dozen of causes. However in this case it is safe to say that this set of events has one common fundamental cause: transatlantic slave trade.
Explanation:
The transatlantic slave trade was a long duration event that completely changed internal dynamics of African empires. Although to say that it destroyed Africa's cultural achievements is too much, it certainly impacted the entire continent.
Africa had internal slave trade since long time before the 14th century. This trade however was small and connected with demands internal to states in the continent. When the atlantic trade started and became routine it was big business, the bigger of the modern era: it was a world trade that was responsible for much of the growing of many entire nations.
The last country to abolish slavery was Brazil in 1888. Transatlantic slave trade started in the 1400s with technological developments that improved navegation and ended in mid 1800s.
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In 1798 the United States stood on the brink of war with France. The Federalists believed that Democratic-Republican criticism of Federalist policies was disloyal and feared that aliens living in the United States would sympathize with the French during a war. As a result, a Federalist-controlled Congress passed four laws, known collectively as the Alien and Sedition Acts. These laws raised the residency requirements for citizenship from 5 to 14 years, authorized the President to deport aliens, and permitted their arrest, imprisonment, and deportation during wartime. The Sedition Act made it a crime for American citizens to "print, utter, or publish . . . any false, scandalous, and malicious writing" about the Government.
The laws were directed against Democratic-Republicans, the party typically favored by new citizens, and the only journalists prosecuted under the Sedition Act were editors of Democratic-Republican newspapers. Sedition Act trials, along with the Senate’s use of its contempt powers to suppress dissent, set off a firestorm of criticism against the Federalists and contributed to their defeat in the election of 1800, after which the acts were repealed or allowed to expire. The controversies surrounding them, however, provided for some of the first testings of the limits of freedom of speech and press.
