What is the link between migration and urbanisation... give examples and explain

Migration, whether internal or international, has always been one of the forces driving the growth of urbanization and bringing opportunities and challenges to cities, migrants and governments. Increasingly, municipal authorities are becoming recognized as key actors in managing migration and have started including migration in their urban planning and implementation.  

For cities to better manage migration, data on migration and urbanization are essential. However, these data are not always available or – if available – not used or accessible at the urban level, nor disaggregated, comprehensive or comparable, particularly in low-income countries.  

answer; ///(b) i believe that the correct answer is it could cause droughts which would make forest fire more likely; /// plz check this answer first, good luck

doctrine that the us had the right to expand throughout north america.