etymology

Tang dynasty in China. (唐王朝・618 AD～907)　
　
This dynasty flourished as a global dynasty.
And this era,many Japanese international students went to China.　
　
Character of "唐".
As result it became one of the words to symbolize China in Japan.
(Although this would not be all of the reasons.)
　
Pronunciation of this character in Japanese is "tō" or "tou". (とう)

About 800 years later，Nagasaki of Japan of the Tokugawa era. (17 century～late 19th century)　
Here was a only trading port with China and Netherlands.　
At that time Japan had adopted a policy of seclusion.　
　
And at that time China was the era of the Qing dynasty. (清王朝)　
But chinese interpreter of Japan side.
They were called "Tō tsūji". (唐通事)　
　
And foreigners were restricted residence.

Chinese residence at Nagasaki.
It was called ”Tōjin machi”. (唐人町)
　
Tō・唐・とう　 jin・人・じん・people  machi・町・まち・town


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Well，China of around 700 BC.
China went to deepen the degree of confusion gradually.
　
And around 500 BC.
China has entered the Warring States era in earnest at last.
　
Country that was terminated this Warring States era.　
It was "Qin"kingdom of most west of China at that time.　(秦)
　
221 BC，Qin unified China.
However，after 15 years this dynasty is destroyed by the Han dynasty.
　
Qin・秦.
Pronunciation of this character in Japanese is "shin".　（しん）
　
"China."
Etymology of this character.
It seems this 秦.
　
And era of the Han dynasty of next.　
China had an interchange with the Roman Empire.
　
The Roman Empire was called 大秦 at the Han dynasty.
Literal translation of 大秦 is "Big Qin".

They called each other as "秦".


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By the way，China had been suffering from the northern ”Xiongnu” from previous. (匈奴)
Xiongnu was equestrian people.
　
But this era, they were finally repulsed the Xiongnu.
As result Xiongnu went away to the west.

Invasion of the Huns.
This seems became trigger the Roman Empire destruction.
(As possibility)