The Empire and the Peninsula
Till the middle of the 20th century or the end of WWII, some European countries, the Russian Empire, and the US invaded Asia and colonized many regions.
But Japan had been closed off to the world. The samurai government had trade ties with only China and the Netherlands in addition to a diplomatic tie with Korea. But, the US sent several naval ships to Tokyo Bay to force the samurai leaders to open the nation.
(The reason why Japan had been sealed off to the world for centuries was that samurais did not want Christianity to prevail in Japan.)
As the Tokugawa shogun, namely the head of the samurai regime, found that his troops could not be well matched against the US fleet due to fire superiority on the American side, he decided to open the nation and conclude a diplomatic treaty with the US. Japan ended its 250-year long separation from the world. But after opening the nation, the Tokugawa clan fell. Anti-Tokugawa samurais taking the emperor on their side launched a civil war to defeat the Tokugawa camp. They formed a new government in the former capital of the Tokugawa regime Edo which was now called Tokyo.
(There were some samurai clans in Japan who had been enemies of the Tokugawa clan since the early 17th century. They were waiting for a chance of reprisal. They found that the Tokugawa shogun failed in handling foreign countries so that Japan opened the door to Western powers.)
Then, the new government of Japan that took over power from the Tokugawa clan started modernization and Westernization of Japan. They especially concentrated on building up modern army and navy, though the samurai spirit was inherited. The new Japanese leaders knew well that the Tokugawa shogun was forced to accept unequal treaties with the US and other Western powers because Japan had less fire power. Without the strong military forces, Japan had to face a danger of being subject to Western rule. So, ex-samurais who formed the new government in the Meiji era (since 1868) pursued a policy of increasing wealth and military power with full efforts.
But this new Japan, namely the Empire of Japan, imitated Western powers too much. It started to behave like one of Western powers. It came to despise other Asian countries, especially Korea and China, as the two countries could not adapt themselves to the trend of time. Korea and China did not now show any sign of success in modernization and Westernization. And as Korea was so close to Japan, the Imperial Government started to interfere in the Korean politics, though Korea was then continuing a closed-door policy like Tokugawa Japan.
The Empire of Japan wanted Korea to develop itself well to be a trade partner of the Empire and a military ally of the Empire. But, the Korean kingdom could not succeed in modernization due to its out-of-date social and political systems. The literacy rate in Korea was less than 10% while it was over 90% in Japan around 1900. For example, Korean soldiers could not read and write but Japanese ones could. Korea could not even make war against Japan.
After a long story, the Empire of Japan annexed, occupied, and managed the Korean Peninsula from 1910 to 1945. But with the end of WWII, the Empire of Japan fell. The Japanese military elites were wiped away from the Japanese Government. Korea came to be independent.
But when Korea left the Japanese control, there were many Japanese assets in Korea. As the Japanese Government did not take back them, Koreans could build the new nation based on industrial and social infrastructures Japanese left in the Peninsula.
The value of those Japanese assets left in Korea after WWII is estimated to be 13 trillion 350 billion yen or $167 billion in today's value.
So, Koreans got factories, plants, equipment, infrastructures, and systems worth $167 billion for free after WWII from Japan.
That is why most of Japanese are disappointed to see rude and mean anti-Japanese behaviors among Koreans today.
Assets of the Empire of Japan Given to Korea after WWII
*** *** *** ***
Mar 7:18 And he saith unto them, Are ye so without understanding also? Do ye not perceive, that whatsoever thing from without entereth into the man, it cannot defile him;