Why might governments put up walls on their borders?

Which of the following was a factor in the development of the english common law ?

Which country was an ally of the united states during world war ii? germany china japan italy

If the ussrs economy has remained agricultural-based rather than industrial, then a. the unemployment rate among men would have been much lower b. women would have been less in demand in the workforce c. crop productivity would have led to larger , better nourished populations d. children would not have had to leave school early to work in factories