What spurred road building in the 20th century?

What would lead a historian to consider two events to have a relationship of correlation rather than causation?

President clinton, on the fortieth anniversary of the events in arkansas surrounding the "little rock nine," stated that "when the constitutional rights of our citizens are threatened, the national government must guarantee them." this principle was the basis for using federal authority in: the expansion of voting rights to women. the passage of the civil rights act of 1964. the passage of the americans with disabilities act. all of the choices.

Explain one major pattern of cultural interaction between nomadic and sednetary socities in afro eurasia before 1450 ce