Austria-hungary and Serbia were the first two nations. However, I do not know much about why the americans joined the war. Sorry.
Answer:
B. To keep one branch of government from becoming too powerful
Explanation:
The checks and balances are between the three branches of the federal government, the executive, legislative, and judicial. To prevent one group from becoming anywhere close to a dictatorship, the other branches can veto, declare unconstitutionality, override decisions, etc.
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Answer:
D.
Explanation:
I'm assuming you mean the Potato Famine in Ireland that lasted from 1845 to 1849? It was caused by potato blight and even spread to areas other than Ireland, leading many Irish to emigrate en masse to other countries-mostly the US.
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Answer:
It increased material wealth, extended life, and was a powerful force for social change. It undermined the centuries-old class structure in Europe and reorganized the economic and philosophical worldview of the West
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