Why was the berlin wall built? i need a few quick facts about what led to the construction. it doesn't need background info or anything, just some facts. update: specific things !

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.