Francisco Pizarro led the conquest of the Inca Empire.
Answer:
Fertile Crescent
Explanation:
It is the Fertile Crescent as the shapes of the river formed a rough crescent shape that was ripe for farming due to the easy irrigation and moist soil.
It would be "Whether a new state or territory should enter the Union as Free or Slave" that had the most impact on the Civil War, since the North was strongly against the spread of slavery, while the South was in favor of it.