NATO Secretary General Jens Stoltenberg has said bonds between Europe and North America have weakened, appealing for an international effort to shore up the trans-Atlantic military alliance. “It is not written in stone that the trans-Atlantic bond will survive forever,” Stoltenberg said ahead of July’s NATO summit. The NATO chief said, in a speech on Thursday in London, that the world faces “an unpredictable security environment due to terrorism, proliferating weapons of mass destruction, cyberattacks and an assertive Russia,” AP reports. “Maintaining the trans-Atlantic partnership is in our strategic interests,” Stoltenberg added.