DTM is not raced only in Germany !! The races are on live TV in nearly every country in the world. Except here....
This year the 12 race schedule....won by AUDI, included Mugello, Italy; Zandvoort, Netherlands; Brands Hatch, England; Barcelona, Spain; and LeMans, France [not the 24HR.] I also believe a final event in Behrain was cancelled this year due to economic conditions. It is generally considered the most popular touring car series in the world.
Current rules call for normally aspirated 4.0 V8's with about 500 HP. They are far from the most powerful touring cars but they might be the most expensive. They easily cost 10 times more than a NASCAR stocker... probably 20 times more. They are technically nearly as complicated as formula one cars...hence the reluctance of firms other than Audi and MBZ to compete, BMW has withdrawn because of cost for example. The rules would not stop American cars or others from competing. In the past Volvo even won the series, as did BMW 6 series when it was known as the German Touring Car Championship. Now it is known as German Touring Masters....DTM.
BTW, several Mustangs privately entered by German Tuners ran various races in the early '90's and the best finish ever was 8th I believe. I attended a race a number of years ago and suggested a well prepared Camaro would be very competitive in 2 years. One to learn the rules and tracks, and one to prepare the car and team. The Germans present told me "no way", and if it did happen the rules would be changed. Plus at that time I did not know how sophisticated the cars would become....I've been told roughly one million per car [rolling chassis], one million per engine and transmission, and one million per electronics/enginemanagement system. A C6R would blow them away on any track but it is not a touring car. You would have to play by their rules .... ie.,home field advantage. But my professional opinion is GM has the ability to be competitive with Cadillac or Chevy.....but not the interest or money.
If you doubt my synopsis check out
www.dtm.de and appropriate a lot of Marks. This is my favorite racing series in the world. And ultra. ultra competitive.