I cannot answer all the questions, but I can answer most of them.
Korean culture in terms of philosophy is a fusion between native Korean religion and Chinese traditions. Many of rank systems were influenced by China, although the Korean Bone Rank system was more restrictive than China w/ some jobs/government positions being limited to people of certain rank. Philosophy was important to Korea, as their currency has two Neo-Confucian thinkers on them. Confucianism highly values education, and the civil service exams were the key to getting a government position. To pass these exams, one had to know the Classics. As a result, education was emphasized.
Technically the political entities that pre-dated the Koryo Dynasty (935 – 1392 CE) were states that invaded and conquered their neighbors, except they are not seen that way by Koreans. It is seen as unification. Silla (57 BCE – 935 CE) for example conquered the neighboring kingdom of Kaya (47 BCE – 562 CE). While both of these are seen as Korean states and part of Korean history, it is important to note, neither Silla nor Kaya saw themselves as related, but as enemies. The concept of Korea did not exist yet.
The Koreans fought a very fierce war against the Mongols earning respect. However, the Korean people, suffered from raid, and double taxation: first from Korean government which fled the mainland to an island, and second from the Mongols. While the Mongols technically never conquered Korea, they did force tribute, which was seen as a form of submission, influenced by the Chinese system.
Attempts to conquer Korea go back far with several attempts by the Steppe tribes, China, and Japan. Only China and Japan were successful in establishing colonies.
Various Steppe tribes were viewed as threats. The Xiongnu (c. 500 BCE – 200/300 CE) were a powerful confederation turned empire that often raided and attempted to steal territory from Koguryo (37 BCE – 668 CE). In the ninth century CE, Parhae became a state, dividing the Korean peninsula in half. Koreans view Parhae as a Korean state that resistance nomadic attacks. Turkic historians view Parhae as a state established by the Malgal that conquered part of Korea. The reality is likely that Parhae was mixture of various nomadic groups from the Steppes and Koreans from the old Koguryo Kingdom. The Khitan Liao (947–1125 CE) attempted some invasion, but was repelled. The Jurchen (1113–1234 CE) were a fierce force. In 1107 CE the Koryo created the Extraordinary Military Corps and pushed the Jurchen back to the Steppes. The Qing before conquering China attempted to invade the peninsula as well but was repelled.
Chinese colonialism starts during the Han Dynasty (206 BCE – 220 CE) with 4 Commanderies lasting from about 100 BCE to 313 CE. The Sui Dynasty (581–618 CE) attempted 4 campaigns that failed and bankrupted the dynasty. The Tang Dynasty (6180–900 CE) aided Silla in unifying the peninsula, but was pushed out by Silla.
Japan has invaded Korea 3 times according to Korean history. First attempt was during the Three Kingdoms Era of Korea, which has various controversies I will not get into. The second attempt was in the 1590s during the Joseson (New Choson or Yi) Dynasty (1392–1910 CE) which was repelled by Admiral Yi. In 1910 Japan invaded and brutally occupied Korea until 1945.
Up to about 1400, Korea resisted due to their military skill and tenacity.
By the time Admiral Yi was serving in the military, the Koryo suffered from repent corruption. The military was in decline. Admiral Yi fought on the border against the Jurchen and had to train his troops well to survive. When Yi took command of the Korean military, he taught himself about military tactics, science, and developed the Turtle ships. Korean historians attribute victory in the war almost entirely to Admiral Yi arguing Koryo would have fallen if not for him.
I do not feel qualified to answer this.
Again, Korea was influenced by China, and had institutions based on Chinese traditions. In 992 CE Korea created the Kukchagam (national university), but Koreans also went to Chinese and Indian universities to study. India is the origin of Buddhism, another major religion in China, Korea, and Japan. Some Koreans served in China’s bureaucracy and retired in Korea, giving their experience to a younger generation.
A group from the Siberian Steppes migrated to the Korean Peninsula known as the Yemaek that mostly replaced the previous population. The Yemaek created many states like Kojoson, Puyo, Okcho, and many smaller states in Manchuria & the northern Korean peninsula around the fifth century BCE. Many Koreans can trace their ancestry back to the Yemaek.
Like my answer to number 1, it has to do with the influence of Confucianism and civil examination system.
I do not feel qualified to answer this.
The Korean War could be seen as a civil war, which would naturally make it much bloodier. Fighting during the U.S. Civil War was also very high due to it being on home soil.
During the rule of King Sejong (r. 1418–15 CE) of the New Choson Dynasty, the Hangul alphabet was invented to increase literacy because Chinese was too time-consuming to learn with its 2,000 some odd characters. Hangul was purposely devised to be different from Chinese language system. Hangul has 26 characters and became extremely popular during Japanese Occupation. It is also responsible for Korea’s very high literacy rate.
Since you are interested in Korean movies, I recommend 71 Into the Fire.
Sources:
Craig Benjamin, Foundations of Eastern Civilization.
Gina Barnes, State Formation in Early Korea.
Henthorn, A History of Korea.
Lee, A New History of Korea.