The sheer scope of the humanitarian disaster so far — more than 150,000 dead, 14 million displaced, 30 million in need of aid — would in years past have at least nudged it on to the western political agenda. Samantha Power, a UN ambassador under Barack Obama and administrator of the US aid effort until this year, had argued in her 2002 book A Problem from Hell that the US political class was always reluctant to condemn mass atrocities as genocide because it could propel Washington into an unwanted military intervention. That was the go-to text for Hollywood celebrities such…