Sorry to sound provocative, but what is to stop the U.S. Greens from making a similar development to the German Greens?
i.e. Wars (Yugoslavia + Afghanistan), demontage of the welfare state, neo-liberal policies, etc.
A friend of mine in the States says that the U.S. Greens even maintain fraternal relations with their awful, awful German counterparts, cooperation with the Heinrich-Böll-Stiftung, etc.
So it's not even the case that the U.S. Greens have as a model the German Greens of 30 years ago; rather, they regard them even *today* as a model to emulate!
So, again, why?
You can have wars and neo-liberalism with Democrats and Republicans. An extra political party is surplus to requirements.