Rationally speaking, the fact may be like this:
* Korean originally had their own language, which was independent from Chinese language.
* During Tang Dynasty of China, Korean adopted Chinese characters in their language.
* At some stage of recent centuries, Korean removed Chinese characters from their language again.
It is not a rare thing in anthropology that different tribes' culture influence each other. The Han tribe Chinese itself has a mixture of many tribes' culture. For example, Buddhism was not from China but was brought to China by those minority tribes that lived in Xi-yu, or the western regions, which are the current Xinjiang and mid-asia. However, it became one of the main religion of whole China.
As for Chinese language, from its several thousands years of history
, it should be said as originated from China instead of from Korea.
As an anthropological fact, many Asian languages have adopted some Chinese characters. It seemed that the Chinese did not colonize them to force this, but that they proactively went to China to learn Chinese culture by themselves during China's Tang dynasty, which was about 1000 years ago.
You can see a lot of Chinese characters in Japanese language. Additionally, the current Japanese culture is nearly a full copy of China's Tang Dynasty culture including its architecture, clothing, food etc.
Vietnamese language also adopted Chinese characters. Then when being occupied by French, I think they made the language latinized.
I actually have found that Koreans are systematically claiming their cultural independence from Chinese culture. It might because when China's economy is fast developing they feel threatened.
The aggressive gesture of China comes from China's governing regime which is still a Communist regime like the former Soviet Union. China's aggressiveness does not come from Chinese culture itself. It is a residue of the confrontation between the Communist camp and the free world camp during Stalin and Mao's time.
The Chinese culture itself is very peaceful and non-aggressive. So take it easy.