Where is the origin of the word old Qin?

My old Qin is from the theme song of the TV series Daqin Empire. The original lyrics are as follows:

Old Qin, * * * caused a national disaster, old Qin, come back to my country. There will be no truce until the blood runs dry! There are great Qin in the west, such as the rise of Japan, a hundred years of national hatred, and vicissitudes of life are hard to level! The world is in turmoil, how can it be good! Qin Yourui who fought with the front line!

Catch up with Shang Yang's political reform and become Qiang Qin, and write down that the smoke of the Chu-Han dispute has been extinguished, and the Daqin Empire with * * * 6115 million words is a masterpiece that Mr. Sun Haohui has worked hard for more than ten years. The adaptation of the TV series "Daqin Empire" can also be described as impassioned and magnificent, showing the unified style of who is in charge of ups and downs and who is left behind. In particular, the tragic theme song sounded, which made people have mixed feelings: lamenting the hard-won reunification of the Qin Dynasty, lamenting the hard-won political reform of Qin Xiaogong Shang Yang, lamenting the hard-won bloody sacrifice of Qin Jun's leading soldiers, etc., and lamenting that our Chinese nation has suffered from national disaster, national hatred, dying struggle and bloody sacrifice for thousands of years.

If the Qin empire lasted longer, or the title of "Han people" is now "Qin people", that is to say, all of us as Han people can belong to the so-called "brave Qin". Therefore, when we talk about the "old Qin" who "went to the national disaster together" and "recovered my rivers and mountains", we can't simply understand it as referring to the Qin people in Shaanxi and other areas in the past, but should talk about the whole Chinese nation involved in the Han civilization for thousands of years.