(by S. Miyauchi, Professional Engineer, Doctor of Engineering, JSME Fellow)
After Mongolia conquered China (Song) and became the biggest empire in world history, they attacked Japan twice in 1274 and 1281 with the world's biggest fleet at that time. Surrender soldiers of China and Korea also rode on it. About war in 1274, this picture is very realistic so that Mongolian soldiers did a group war with not only composite bows but also grenades. And Japanese horse was surprised at those sounds. In 1281 Japan built stone wall on the seashore and blocked the Mongolian army to land. At that very moment, a typhoon (Someone called the wind of God) struck Mongolian to withdraw.
As is this typical case, China and Korea had always been threatened by northern equestrian people such as Huns, Mongolian and Jurchen, but Japan is historically difficult for foreigners to invade. And there has been few ethnic and religious conflicts. Obviously because it is surrounded by the ocean and it has severe weather conditions (typhoon in summer, heavy storm and snow in the Sea of Japan due to Siberian seasonal wind).
The only threat now is the first one shot from North Korea. Because Japan might be already within range of a little high performance missiles than V2 rocket. Also the threat by nuclear weapons which Japanese peeople hate for the tragedy of Hiroshima and Nagasaki is very unpleasant. Because the deterrence force might be sufficient with the latest weapons (fighter aircraft and cruise missiles), the faith of nuclear weapons such as North Korea is very strange.