What caused the development of in the us!??

Judging from all the hype, the economic book of 2016 is Robert Gordon’s The Rise and Fall of American Growth. Gordon’s book offers the definitive account of how the many technological innovations between 1870 and 1940 dramatically improved life in the United States. On the positive side, he accurately chronicles the major advances in electricity, public sanitation, pharmacology, and communications—and documents the rise of the internal combustion engine. But on the negative side, the book is utterly silent on why American society was capable of making such a radical transformation during that period.

Gordon’s book has attracted much attention because of his warning that America is not likely to again see such dramatic improvements in the standard of living. The question is why. The first part of the answer is simple enough. In the late nineteenth century, there was a lot of low-hanging fruit—that is, there were many ripe opportunities for innovation. This partially helps explain why American society grew in the years between the end of the Civil War and the start of the Second World War. The second part of the answer, which Gordon leaves unmentioned, is that these innovations coincided with a period of American history when laissez-faire capitalism was at its peak. Growth started to decline because of the massive expansion of the government occasioned by the New Deal, which put a strain on the free market.

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option d is correct. corroborated sources of historical evidence   is necessary to validate a claim about an event in history.

historians tend to use written sources, but audio and visual materials as well as artifacts are important objects that supply information to modern historians.

historical sources are usually divided into two categories: primary and secondary sources. depending on the historian's intent, some sources shift their designation. determining what type of sources toimplement, and the level of credibility and reliability of those sources, is a significant step in critical thinking for the historian.

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