For the past five years, the Sudanese regime has been waging a war against its own people in Darfur. Tactics have included the indiscriminate murder of civilians, collective punishment, burning of villages, rape, ethnic cleansing, and the use of starvation as a weapon. In response, Sudan has been isolated from the international community. It has been subjected to international sanctions, and its leaders have been indicted by the International Criminal Court.
For the past two years, the Ethiopian government has been waging a war against its own people in Ogaden. Tactics have included the indiscriminate murder of civilians, collective punishment, burning of villages, rape, ethnic cleansing, and the use of starvation as a weapon. In response, the international community has turned a blind eye and remained silent. The Ethiopian regime continues to receive almost US$2 billion of aid a year.
What's the difference here? A major one is that the Ethiopian government is a major ally in the US's war on terror, and acting as its proxy in Somalia. And for that, the US and its allies will forgive a lot. Even an ongoing crime against humanity.