In the Dan 2:39 it says: "another kingdom inferior to thee"

Dan 2:39 And after thee shall arise another kingdom inferior to thee, and another third kingdom of brass, which shall bear rule over all the earth.

In what way would this kingdom be inferior?

I know silver is inferior to gold, but if that is the meaning then doesn't it stand that each of the other two nations will also be inferior to each other. The fourth then would be least of all, yet the fourth nation seems more in strength then all the others.