There are hundreds of Mario Monti wanna-bes. And most do not even live in Europe.
Monti is the European Competition Minister who was the thorn in General Electric's side and is now reeking havoc on Microsoft. He represents the EU's will and no major companies can merge without his blessing.
After Monti there are American regulatory bodies (DOJ, FTC, FCC, etc) that often have to sign off on a merger. But basically, that's it. Any company really has to only worry about the EU and the US.
But that's changing.
As we increase the number of actors on the world stage that approve the merger process or that can investigate/enforce anti-trust issues, we are going to create a regulatory log-jam.
China, Japan, Latin America, India, Russia, might soon get in the game -- especially if one of the merged companies has some significant interest in their country.
There are some solutions on the horizon. The ICN (International Competition Network) has a world membership that looks to resolve these disputes. But it is a nascent organization that has yet to be tested.
To overcome these jurisdictional issues, we will have to create some sort of world arbitration system that regulates anti-trust concerns. And no country will be happy with the ultimate compromise and encroachment on sovereignty.
My guess is in the mid-term, this will significantly reduce the market cap of global companies that were once thought to be acquisition targets -- because acquiring them will be very difficult.