At least 100 Americans have gone — and some continue to go — to Syria to fight against ISIS. Many have joined a Kurdish militia group called the People's Protection Units or the YPG. What these volunteers are doing isn't illegal, but it raises many questions.
Over 600 people including ISIS fighters and their families were escorted from the Lebanon border by Syrian government forces. That angered the US, which launched airstrikes to block their path to a town near Iraq.