SEOUL, South Korea — The United States, South Korea and Japan opened an air and naval exercise off a South Korean island Monday in their latest joint drill condemned by North Korea as a “reckless show of strength.” The exercise called Freedom Edge is aimed at strengthening the countries’ combined operational capabilities in the sea, air and cyberspace and is necessary to counter North Korea’s growing nuclear and missile threats, South Korea’s Defense Ministry said. The U.S. Indo-Pacific Command