What caused europe to switch to the feudal system?

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.

Me i really need which of these was an accomplishment of the han dynasty? the invention of the seismograph finding a water passage to europe the invention of the ballpoint pen the invention of the abacus

Which physical feature minimizes population density in northern africa?