What, in addition to geographic boundaries, might have kept the people of the huang river civilization from traveling to far-distant regions?

they feared that their bronze weapons would be no match for the iron weapons of ancient egypt.
they could get everything locally that they needed to survive and grow.
they had learned about the other river valley civilizations but feared contact would bring invasion.
they had not yet developed a system of money based on coins.

the answer is richard nixion

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.

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