Many languages, one language

In human evolution, the advantage of having many different languages and dialects was that it enabled each village to tell "ours" from "not ours". The advantage of a uniform language over broader area is that it facilities trade and other positive interaction. (Wow! Those girls from the Furry Squirrel village......)
Nowadays, having a different language provides little useful defense that is not provided by other means (passports for example), but the advantage of people able to participate in global trade is enormous. (There are also major advantages to being able to pick and chose which trade to take part in, but you need to be able to participate in the first place to be able to pick and chose.)
This suggests that there is a force pushing people toward a unified language. Right now that language is English, but a global English could evolve that is distinct from American or British or any other national English. Particularly if the United States continues to prefer the front lines of pointless wars over the front lines of knowledge.