Written by John Tirman - It is ever more clear we are in the midst of a colossal migration crisis. In Europe, the haunting specter of hundreds, even thousands, of Africans drowning in the Mediterranean has captured headlines for a few days. European leaders, who had tried to discourage crossings by withdrawing naval patrols, will be forced to reconsider on humanitarian grounds. A similar situation shamed the United States last summer, when tens of thousands of Central American teenagers and even younger children traversed Mexico atop trains to escape violence and poverty. With spring, they are coming again.