[citation needed] Copper deposits are recorded as having been discovered in the area around the year 1550, but exploitation did not begin until two local households received an official permit in 1610 to establish a mine.

Copper, including that produced at the Ashio mine, played an important role in the solidification of Tokugawa rule in the early part of the 1600s and later became Japan's chief metal export after 1685.

It became privately owned in 1871 following the industrialization initiated by the Meiji restoration, by which time production had dropped to less than 150 tons per year.

A year later, the mine was producing over nine million tons, and by the end of the century, it accounted for 40 percent of Japan's copper production.

[1]: 89  During the Meiji period, arsenic trioxide became a major secondary product of the mine, and large amounts of sulfuric acid was also used for minerals extraction.

[5] Residents of the surrounding area also suffered multiple health issues, including sores where they came into contact with contaminated water or soil, chronic arsenic exposure, higher premature death rates, lower birth rates, and in the case of many women, trouble producing milk.

[1]: 90–97 At the same time as the environmental damage was occurring in the Watarase River valley, the Ashio Copper Mine was expanding and modernizing.

The new processing methods caused additional problems: Mass extraction produced piles of slag, which rainwater ran through and from which it absorbed chemicals.

In 1891, after the disastrous 1890 flood, he gave a speech on the floor of the Diet calling on the government to close the mine because of the pollution.

In February 1897, Tanaka delivered a speech questioning Enomoto's behavior, which gained him support from several notable figures.

After visiting the area surrounding the mine and seeing the damage for himself, Enomoto eventually created a Pollution Investigation Committee.

In addition, the government, headed by Ōkuma Shigenobu, put[vague] plans for reforestation of the area surrounding the Ashio Copper Mine.

While Tanaka was prevented from handing over the letter, its contents were published by national newspapers, helping to publicise the plight of residents, which prompted the government to act.

[6] The 1907 Ashio Riot occurred February 4–6, 1907, involved pit miners who had been demanding higher wages,[2]: 99–108  and targeted mostly infrastructure and low-level mining officials.

The miners then began to leave the mine pits in groups and assembled in front of cabin[vague] at the entrance.

Other miners who were still underground began to come aboveground later in the afternoon, when they gathered in front of the Tsūdō office and threw rocks at the windows through the evening, at which point the rioting ended for the day.

[2]: 99–100 Early the next day, miners attacked the cabins at the Sunokobashi mine pits, threatened the staff there, and cut telephone lines.

The extent of the damage from the first two days of the riot included several cabins and barns, eight trucks, a few drills, and the injured officials.

[2]: 100–101 At the Honzan Ariki mine pits, miners destroyed the underground foremen's cabins early in the morning before moving aboveground in two groups.

[2]: 109–112 In the days after the mine resumed operations on February 13, miners at Kodaki, the only pits where rioting did not occur, became increasingly uneasy.

On February 26 the new mine director, Kondō Rikusaburō, informed the miners at Kodaki that they would be receiving bonuses for their non-involvement in the riot.

The wage increases were officially announced on March 1 and involved an average raise of 19.4 percent and improved financial provisions for absences related to injury or illness.