Who, specifically, did Yanagida mean by "half the world"?
In the manga, in chapter 7, Yanagida mentions:


  Is there something here that's worth turning America, China, and Russia... half of the world into our enemies?


It's been mentioned that (emphasis mine): 


  The major powers, China, the European Union (EU), India, Japan, Russia, and the United States, contain just over half the world's people and account for 75 percent of global GDP and 80 percent of global defense spending.


So he's likely to mean most of developed countries that are world powers. Most notably America, China, and Russia.