The fast-deteriorating situation was set in motion last week, when Trump ordered U.S. troops in northern Syria to step aside, clearing the way for an attack by Turkey, which regards the Kurds as terrorists. Since 2014, the Kurds have fought alongside the U.S. in defeating the Islamic State in Syria, and Trump’s move was decried at home and abroad as a betrayal of an ally. Over the past five days, Turkish troops and their allies have pushed their way into northern towns and villages, clashing with the Kurdish fighters over a stretch of 200 kilometers (125 miles). The offensive has displaced at least 130,000 people. On Sunday, U.S. Defense Secretary Mark Esper said all American troops will withdraw from northern Syria because of the increasing danger of getting caught in the crossfire.