This is the 19th most frequent Chinese word.
中国
"China"
Here, '中国' refers directly to the country of China as a proper noun.
中国是一个历史悠久的国家。
China is a country with a long history.
Here, '中国的' indicates possession or association, meaning 'of China', relating to traditional art being connected to China.
我们需要学习中国的传统艺术。
We need to learn about China's traditional art forms.
Here, '中国' is used as an adjective to specify the origin or type of the culture being referred to, i.e., Chinese culture.