"Missing in action" has always been a problem in warfare. Until the last few centuries, soldiers didn't carry any identification. And in large battles, with thousands of dead, the bodies were generally quickly stripped and buried in mass graves. Even with the introduction of identity tags in the last century, bodies were still lost in jungles and swamps, or remote air crashes. Artillery literally blew soldiers to pieces. But as more technology arrived on the scene, it became easier to find lost remains, and identify them. Ground penetrating radar and DNA analysis make it possible to find long lost "unknown soldiers" and identify them. While much is made of the energetic efforts to find Vietnam era dead, the desire to find and identify battle dead is even stronger in other cultures (that put a high premium on venerating the dead.) A case in point is Vietnam, where elderly parents and siblings still journey to remote battlefields to look for their dead, and to pay their respects even if nothing is found. Japan, like most east Asian cultures, shares this custom, and relatives of World War II Japanese dead still journey to Pacific island battlefields to honor their dead. As DNA analysis becomes cheaper and more capable, and improved sensors discover more bodies, expect to see an increasing number of "Unknown Soldiers" found and put to rest.
