Long ago in the 1500's, Korea was under one nation living peacefully under monarchy. However, one day, the Japanese decided that they wanted to invade China. Korea was under alliance with China at the time, and refused to lend their land to the Japanese for them to travel through Korea to wage war on China. However, Koreans, who always keep their promises, refused to let Japan through. Therefore Japan decided to wage war on Korea and conquer us before going to China (Fk you Japan). Japanese military was in its prime at the time, and Korea lost their land to Japan very fast. When China got the news that Korea has fallen in a very short amount of time, they had thought that Korea colluded with Japan and that we had broken our promise (Fk you China). This long war ended in a peace treaty between the Japan and China.
Now come 19th century, Japan thinks that they should wage war again (Fk you Japan). They conquered Korea again in order to wage war on China. They tried to erase our identity (Fk you Japan). They disallowed use of our language (Fk you Japan), forced us to pray to their gods (Fk you Japan), forced us to build Japanese shrines (Fk you Japan), forced us to adopt a Japanese name (Fk you Japan), and conscripted Korean men to fight their war (Fk you Japan) and conscripted Korean women to be their sex slaves (FK YOU JAPAN). Then outside forced intervened such as USA, and they nuked the shit out of Japan. Following soon after, the WWII ended and Korea was at last free of Japanese rule. However, because Korea lost all of its identity, its independence spelled chaos and turmoil. Half of the nation was split towards democracy, and the other one was leaning towards communism. You can guess which one is which. Democracy = South Korea, Communism = North Korea. And then there was internal war again.
After the demonstration of nuclear warfare, the Cold War had begun between USA vs. Russia. Because of globalization, USA could not afford to directly fight Russia. Therefore, they used Korea as a medium to carry out their battle. USA supported South Korea, Russia supported North Korea. The Russians provided the North Koreans with tanks, and nuclear research notes (Fk you Russia); this is actually the reason how North Korea started their nuclear research and why things are such a shitfest right now. FK YOU RUSSIA! Meanwhile, USA provided South Korea with NOTHING (FK YOU USA). Naturally, North Koreans quickly invaded South Korea. After seeing how stupid USA was, they finally decided to send real help to South Korea, and fended off the North Korean advance.
Now coming towards near the present time, the South Koreans adopted the USA democracy, and is economically growing because they are open to international trade and focusing on STEM-related research. Meanwhile North Korea, under the same rule of the same family for 3 generations, has not learned their lesson, and continues to isolate themselves from the world and continue their nuclear research that was started because of Russia (Russia fk'd over the rest of the world. Fk you Russia!). That is why North Korea is suffering as a nation. But the take away here is that the division of Korea, and the reason why North Korea is such a pain in the ass right now is because of outside forces continually intervening and not minding their own business. But it can also be argued that South Korea is this advanced with the highest average IQ worldwide because of the influence of Japanese and USA technology. But then... was it worth the millions of lives and the consequences of very tragic events? Perhaps it's not worth debating and just accepting what is reality...
Tl;dr: Koreans are kind-hearted and rest of the world is fk'd up