The events above could be included in an essay summerizing which era in U. S. history?

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.

explanation:

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

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c. troops marched forward in close formation against newer, more accurate weapons