What is your purposed mechanism/leagally authorative/enforcing body to stop two multinational corporations from incorporating in any one of their markets?
Even if they where headquarterd in US and strictly trading on US market, corporations have rights akin to human beings.
Con-agra, unliver, comcast. All these merged in the US just fine under a very stringent FTC. How could they possibly prevent a foreign multinational corp from doing the same?