Since the Syrian civil war began in 2011, no country has felt the pain of the ensuing humanitarian crisis more severely than Turkey. We took in 3.6 million Syrian refugees—more than any other country—and spent $40 billion to offer them education, health care and housing. Our culture of hospitality compelled us to shoulder the burden of hosting millions of war victims with very little help from the international community.

Yet at a certain point, Turkey reached its limit. My administration repeatedly warned that we would be...