Eli Whitney was an American inventor known for inventing the machine that separates the seed from the cotton, called cotton gin. During a period of political instability, the War Department of the USA approved a contract of weapons purchase, and Whitney obtained the contract.
But the problem was the inventor never manufactured a gun in his life. The solution he had was the adoption of standardized parts to accomplish his task. This process created precision equipment that allowed the production of large numbers of identical parts quickly and at a comparably low cost. This new method transformed the manufacturing industry and contributed considerably to the US victory in the Civil War.
In conclusion, in order to attend the contract with the government and to multiply the number of guns produced, Eli Whitney had to resort in the standardized or interchangeable industrial development.
This sentence technically doesn't contain an error in verb-noun agreement, however the noun "each one" is odd here. It should be "everyone"
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The Stamp Act of 1765 was significant in the sense that it was the first direct tax imposed on American colonists (So, 
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