Ri Sang Chol last saw his mother when he was four years old. Now he is 71. His 92-year-old mother, Lee Keum-seom, strokes his wrinkled cheeks and weeps. They are finally together after more than 65 years!

North and South Korea used to be just one country: Korea. Korea split in two at the end of World War II. The Soviet Union occupied the northern portion, and the United States the southern. Negotiations failed to unify Korea, leading to two separate governments being formed in 1948—a communist North Korea and a democratic South Korea.

In 1950, North Korea invaded the South in an effort to forcibly unify the Korean peninsula under communist rule. The fighting stopped in 1953. But the Korean War didn’t really end. The two countries agreed to an armistice—a promise to stop fighting for now. People in the North and South—even within families—were separated, most of them for good. Some North and South Koreans live less than an hour apart. But the two countries are divided by the Korean Demilitarized Zone—a two-and-a-half-mile wide strip of land in which no one is allowed.

People who live in the North or South are not permitted to see each other. They cannot even send letters, emails, or call lost family members on the phone.

Occasionally, North and South Korean officials try to create a more peaceful relationship between the countries, which are technically still at war. This summer, they let a few hundred separated family members have short reunions. Dozens of elderly South Koreans crossed the border into North Korea. They met with their North Korean family members at North Korea’s Diamond Mountain resort. The families spent a week together. But the peacemaking comes late. Most of the people are very old. They know they will probably not see their relatives again before they die.

Mr. Ri shows his mother, Mrs. Lee, a picture of his father. (The mother and son have the same last name. “Lee” is spelled “Ri” in North Korea.) His father cared for him after his mother was separated from the family when they ran away to the South. “Mother,” he says, “this is how my father looked.” Mrs. Lee wants to know how Mr. Ri’s father raised him. Does Mr. Ri have any children of his own? That is just the beginning of her questions. Imagine how much the two have to talk about!