Around 12 minutes through Episode 4, It shows an Asian-looking (possibly Chinese?) President (Dechou Dong, as the intro badge says) in a car, discussing The Gate with his secretary:
President Dong: "Why did the gate open in Japan? We're the ones who need it, don't you think?"
Secretary: "That's correct, President. We can't let Japan have it all to themselves."
President Dong: At first, we'll maintain friendly relations with Japan, and see where this goes. Ideally, I'd like to send half our population to the Special Region."
In Episode 2, around 14 minutes in, you see the American President (noted by the flags beside him) also discussing it with his secretary, saying
President: "The Gate is the new frontier. There must be more resources on the other side than we can imagine. It's a treasure trove."
President: "How about it? Why don't we send our army in?"
Secretary: "That might not be a good thing. Many nations anticipate Japan's defeat. We ought to let Japan take the risks for us."
President: "Yeah, we should avoid having our nation seen as an accomplice."
Where the following image is shown:
Showing people openly protesting against invading the Special Region.
It seems the world's powers are either in it for unclaimed space, or resources.
Most likely, when Yanagida says half the world's people, he either means people will be divided on which side to take, or, the world's powers will either to decide to get involved, or condemn the actions of Japan.
Most probably, the world's powers.