On the day Samantha Power landed in Ethiopia this week, its civil war — now escalating and spreading beyond the northern region of Tigray — entered its 10th month.

Amid allegations that Ethiopian troops and their allies have committed war crimes and ethnic cleansing and have driven parts of Tigray into famine, the United States has already withheld security assistance and effectively banned travel for top officials.

But Power, who is in charge of the U.S. Agency for International Development, or USAID, holds the biggest American lever of influence over Addis Ababa: more than $1 billion in annual aid ranging from health and education support to food and emergency humanitarian response, which makes the United States the largest aid donor to Ethiopia.