Like most 75-year-olds, NATO needs some help reaching out to the younger generation. The military alliance is this week wrestling with such heady topics as the eventual accession of Ukraine and the ailing health of the octogenarian U.S. president. To stay relevant in the modern era, it has turned to a group of 20-something influencers to spread its message. The North Atlantic Treaty Organization invited 16 content creators from countries including the U.K., Germany and France with followings on TikTok, Instagram and other social-media platforms to attend its summit in Washington on July 9-11.