What causes changes in the economy over time?

What would be considered a secondary source about the assasination of abraham lincoln

What event, more than any other led to wwi?

Which reason best explains why certain areas of southwest asia have low population density? a. the semi-arid climate makes farming difficult because it produces very little rainfall. b. the moist climate limits job opportunities because it reduces oil production. c. the semi-arid climate produces heavy rainfall that contributes to devastating floods. d. the moist climate reduces agricultural production by causing water shortages.