But US can not really do anything. We've got troops still in Afghanistan, the people are sick and tired of over a decade of "pretend nothing is happening" war stance, it's been tremendously expensive and increased the debt to crisis levels. And when we have intervened militarily in the last few decades, especially when being in charge, it's been horribly planned and executed. It's impractical to take on another war, especially a war that is guaranteed to spread to multiple countries.
Like the Yugoslavia break up, this needs to be handled by Europe with America only there as a NATO ally. We don't need to be charging in shouting "We're in charge!"