Which of the following is a true statement regarding frontiers? a. maps establishing european frontiers only began to appear in the 18th century. b. prior to a demand for better precision, it was usually rivers that defined new political frontiers. c. maps were never used to illustrate the power of rulers. d. duller colors are always used in political maps to distinguish important regions.

The answer is A. Maps establishing European frontiers only began to appear in the 18th century. With the emergence of territorial states in the sixteenth and seventeenth centuries borders began to be discussed in the context of state ideology. Different topographical features, not only rivers,  but mountains and manmade landmarks such as fortresses, etc. began to serve as borders.  

In the sixteenth century there was a noticeable change in connection with the depiction of political borders on maps. But with the improvement of measurement techniques in the eighteenth century, the concept of "border" acquired linear form. Linearity expressed frontiers.  

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.