Seoul, South Korea CNN  —  Japan is facing its most severe security environment since World War II as three potential adversaries in East Asia – China, Russia and North Korea – ramp up military activities in the region, the country’s defense minister said Tuesday. “The existing order of world peace is being seriously challenged, and Japan finds itself in the most severe and complex security environment of the post-war era,” Defense Minister Gen Nakatani said in an introduction to the ministry’s