Migration caused by climate change and political instability has driven thousands from their homes across North and South America, resulting in an unprecedented number of individuals seeking to cross the border into the United States. The United States, wealthier and with plentiful labor available, still remains a key location for the displaced and desperate. Border states started busing immigrants to northern cities in recent years, some say as a political statement. Some sanctuary cities that initially welcomed immigrants did not have enough resources to house the influx of people and had to ask for more resources from the federal government to accommodate them. This issue of The Reference Shelf looks at the debate over policing the nation's borders and weighs efforts to address migration as a problem against the exploitation of border fears as a political tactic.