The use of belts instead of suspenders began to gradually gain popularity in the 19th century, but it was especially during the late 1800s and early 1900s that belts truly took over as the primary means of keeping pants up.
Previously, in the 1700s and early 1800s, suspenders (or braces) were more common, especially among men, and were considered both practical and stylish. They were often made from elastic materials, leather, or fabrics that could be adjusted to keep the trousers in place.

The pants used suspenders and tightening at the back - practical for hard work in the mines and gold extraction.
Belts began to receive more attention at the end of the 19th century, and the industrial revolution played an important role in this shift. New production methods for leather and metal made it easier to create sturdy and practical belts. Additionally, the belts, as we know them today, became a more accessible and common option, especially as pant styles began to change in line with fashion.
In the 1920s, belts began to become more standardized, and suspenders gradually became less popular, especially in more informal contexts. Today, belts are the most common choice for keeping pants up, while suspenders are often associated with formal attire or as a fashion statement.