Simple, You CANNOT import a vehicle that was not originally sold in the UNITED STATES unless it is at least 25 years old. There are a few exceptions for R&D, car shows, race teams, campers imported for one year of travel, etc., but if you are a U.S. Citizen and want to keep, use and register the vehicle here, it must be 25 years old to legally import into the USA.
It has nothing to do with EU regulation, emissions, crash testing or anything else of the sort. Now, that said, there are vehicles here NEWER than 25 years, that were not originally sold in the US. So, there are ways of getting around it. Some easy, some complex and expensive, some blatantly illegal.
You will want to hire a reputable customs broker, preferably one who is familiar with importing vehicles from the country you are purchasing from and the type of vehicle you are buying. You could also contact companies like Eurotruck or Vermont Unimog and see if they would be willing to buy the vehicle for you and then you buy it from them as a used car, with all of the proper tag, license, docs, etc already completed.
I have never done it personally, but have some friends who have and it is not a fast, simple or easy process by any means.
