Nations make war with surprising ease. Making peace is often much harder. People's opinions must change radically, which is not easy when there is a past history of bitterness, cruelty, and injustice.
That is what makes this month's meeting between the leaders of South Korea and Japan so important.
When President Chun Doo Hwan of South Korea arrived in Tokyo, the Japanese capital, on Sept. 6, it was the first time in almost 40 years that a South Korean leader had set foot on Japanese soil on an official visit.
The reason it has taken so long is that South Korea has felt very bitter about what Japan did to South Korea in the past.
Japan in the eyes of most South Koreans was a cruel master when imperial Japan made Korea one of its colonies back in 1910. That rule lasted until Japan was defeated at the end of World War II in 1945.
Today we no longer call Japan ''imperial Japan'' because the word imperial refers to empire. For Japan that empire collapsed in 1945, although the country still has an emperor, Emperor Hirohito, who is the world's longest-surviving monarch. He was emperor even before World War II began. According to Japanese custom the emperor was divine. But that custom no longer holds true. Nor does the emperor rule anymore, although he and the royal family live in a palace and are the most respected people in Japanese life.
The real power - that is the power to make decisions that affect the lives of all Japanese - lies with Prime Minister Yasuhiro Nakasone, his Cabinet, and the Japanese parliament, called the Diet.
Since they are the most important public figures in Japan, both Emperor Hirohito and Prime Minister Nakasone took it upon themselves to apologize to President Chun for what Japan had done to his country.
During the time of colonial rule, Japan forced Koreans to give up their own language, made them adopt Japanese names, and brought thousands of Koreans back to Japan as slave labor. Any resistance to Japanese rule was put down very firmly.
To help wipe out that memory, Prime Minister Nakasone told the South Korean leader: ''There was a period in this century when Japan brought to bear great sufferings upon your country and its people. I would like to state here that the government and people of Japan feel a deep regret for this error and are determined firmly to warn ourselves for the future.''
President Chun - Koreans are called by what we would describe as the first name - said he had come to Japan to ''open a new chapter as partners.''
Today feelings between South Korea and Japan have improved noticeably. If it weren't so, the South Korean leader would never have made that recent trip to Japan.
Less likely, in fact highly improbable right now, is a visit by a South Korean leader to North Korea.
The two countries that were once united as Korea are divided by the 38th parallel.
The division came about at the end of World War II when the overall ruler, Japan, was defeated. The northern part of the country was controlled by the Soviet Union. It later handed over control to communists who now govern what is North Korea. The United States took charge of the south but ended its control to make way in August 1948 for an independent and strongly anticommunist government.
Less than two years later, on June 25, 1950, the North Korean Army crossed the 38th parallel without warning and attacked South Korea. The South Korean capital, Seoul, which is close to the border, fell in six days.
The war brought the US, Britain, and other countries of the UN in on the side of the more numerous South Koreans (today's population 38 million). North Korea (18 million people today) had the backing of China.
The war raged on for three years and finally ended with a 1953 peace treaty, which stabilized the two countries along the line of the 38th parallel.