Do what Trump and Merkel did - pay off the folks who are letting them cross their country to get to ours. Trump told Mexico he'd tariff all Mexican goods at 50% unless they did something at their Southern border, and it reduced the caravans. Merkel/EU paid North African countries to stop them at their Southern borders and it ended up disrupting the refugee business in countries like Niger where most were coming through. That and maybe start prosecuting/deporting anyone who breaks the law and enters illegally.