http://www.wsj.com/articles/antitrust-suit-over-staples-offi...
Intel for example has / had a practical monopoly in processors for many years in PCs. The government was ok with it, based on various terms they agreed upon with Intel. The same is true of Microsoft, and countless other businesses (big and small) across the US.
There of course used to be far stricter rules on local monopolies in media (radio, tv, newspapers, cable stations etc), but those have been heavily relaxed in the last 20 years.
Market sizes vary. For airlines they look at cities or even specific airports. it doesn't matter that there are a million different airlines, if your merger creates a quasi monopoly for flights into and out of some cities. That's why in airline deals, you often see one of the two sell off routes to third party competitors.
But for chemicals and agriculture supplies--it's really an international marketplace. It doesn't really matter if they are the only US company as long as Chinese, Korean and German companies are active in selling in America.
Though the DOJ will undoubtedly look at the deal hard. Make sure things like distribution chains, retail deals etc. don't create a monopolistic effect.
(Potential supply disruptions might also be an issue, seeing as how last time I checked Germany gets most of it's natural gas from Russia through pipelines going through Ukraine, and with the latter two being at war right now....)
I wonder how come BASF and Bayer are still in business, post-WW2. From the wiki page of Carl Wurster (https://en.wikipedia.org/wiki/Carl_Wurster), the guy who re-established BASF in the early 1950s, out "of the ashes" of the infamous IG Farben:
> Wurster retained links to those he had worked with as part of the Nazi war machine and on 6 February 1959 as chairman of BASF he hosted a reunion banquet for the veterans of the pre-1945 IG Farben Vorstand. The event was attended by Otto Ambros, Heinrich Bütefisch, Fritz Gajewski, Max Ilgner, Friedrich Jähne, Carl Krauch, Hans Kühne, Wilhelm Rudolf Mann, Christian Schneider and Fritz ter Meer as well as Carl Bosch's widow.[4]
All of those guys were Nazis, some of them convicted war criminals.