translation about USA

[atabitaraf]

I've read it from "wikipedia" I can't understand the meaning of "ranked last among" would u plz give me a point?

In 2008, the United States spent a net $25.4 billion on official development assistance, the most in the world. As a share of gross national income (GNI), however, the U.S. contribution of 0.18% ranked last among twenty-two donor states.

[SoothingDave]

On a list of 22 states which donated money, the USA is last on the list.