U.S. Marines, left, and South Korean Marines, wearing blue headbands on their helmets, take positions after landing on the beach during the joint military combined amphibious exercise, called Ssangyong, part of the Key Resolve and Foal Eagle military exercises, in Pohang, South Korea, Saturday, March 12, 2016. North Korea said Saturday its military is ready to pre-emptively attack and “liberate” the South in its latest outburst against the annual joint military drills by the United States and South Korea. (Photo by Kim Jun-bum/Yonhap via AP Photo)

A Ukrainian serviceman fires a 2S7 Pion self-propelled gun during military exercises near the village of Divychky in Kiev region, Ukraine, October 21, 2016. (Photo by Valentyn Ogirenko/Reuters)

In this photo taken Saturday, January 24, 2015, a child makes a face while having her photo taken with the snow covered slopes of the Nanshan ski resort behind her in Beijing. As Beijing makes a final push in its bid for the 2022 Winter Olympics, Chinese President Xi Jinping says winning the bid will encourage over 300 million Chinese to take up winter sports by 2022, according to state-run Xinhua News agency. (Photo by Ng Han Guan/AP Photo)

Robot couple Xiaolan (L) and Xiaotao carry trays of food at a restaurant in Jinhua, Zhejiang province, China, May 18, 2015. The restaurant, which opened on Monday, has two robots delivering food for customers. The robots were designed as a couple, Xiaolan and Xiaotao, according to local media. (Photo by Reuters/Stringer)

A tourist poses for a souvenir snap in front of autumn foliage in Pitlochry, Scotland, Britain on September 28, 2018. (Photo by Russell Cheyne/Reuters)

Participants from a North Korea military band perform during the Spasskaya Tower international military music festival in Red Square in Moscow, Russia, Friday, August 23, 2019. (Photo by Alexander Zemlianichenko/AP Photo)

A woman walks with her daughter through an empty street on April 27, 2020 in Malaga, Spain. Since April 27 children under 12 are allowed to come and go from their homes more freely. Spain has had more than 209,000 confirmed cases of COVID-19 and over 23,000 reported deaths, although the rate has declined after weeks of lockdown measures. (Photo by Daniel Perez Garcia-Santos/Getty Images)

A swimmer swims by a swan in The Serpentine in Hyde Park, following the outbreak of the coronavirus disease (COVID-19), London, Britain, May 26, 2020. (Photo by John Sibley/Reuters)