How long have the Ainu people inhabited Japan?

It is commonly held that about 1000 years ago the Ainu ethnic group established the "Satsumon culture," which encompassed a region spanning Sakhalin, the Kuril Islands, Hokkaido, and northern Honshu.
The Ainu are the aboriginal people of Japan.
The Ainu were long dependent upon nature, making a livelihood from hunting, fishing, and gathering.
However, beginning in the 15th century, with invasions bv the Japanese whom the Ainu called Wajin, the Ainu's vast natural lands were gradually taken from them.By around the 18th century, a series of vicious clashes led to the complete subjugation of the Ainu people by the Japanese.
Following the establishment of the Meiji government, policies encouraging assimilation with mainstream Japanese were implemented, threatening the existence of the Ainu as an ethnic group.
The Ainu culture and language once faced extinction, but the government passed the Ainu Culture Promotion Law in 1997 to promote and protect the Ainu culture.