When did men start wearing belts? And when did they stop wearing braces? It happened, but why and when? The answer is, they didn’t. Braces have gone in and out of fashion over the last 80 years but have always remained in the backdrop.
The picture below, taken from an American 1940s catalogue, shows men wearing belts with Hollywood waist trousers.
The function and allure of braces is undeniable. Consider the elegance of your high-waisted trousers hanging from the shoulders, undisturbed by a cinched waist or a tight pinning wrinkles caused by an ill-fitting belt or narrow waistband.
When your trousers are cut full and with plenty of room to hang, braces serve to maintain the natural flow and drape of your high-waisted trousers, leading to a fluid, harmonious aesthetic.
Catalogues of the period almost entirely show belts with casual trousers; we do not see what men are using for their business / formal trousers, because their jackets are buttoned up. They may be wearing braces, or not. We have to remember that braces were regarded as an underwear component at the time, so were seldom seen (and men wore waistcoats in an age when heating was a luxury).
Military uniforms in WW1 had braces; British WW2 battle dress uniform trousers had braces, but shorts did not (hence no braces in the 8th Army). US uniforms also came with braces, such as these (made of webbing), but were not worn when in shirtsleeve order:
Dugdale Brothers (the mill and merchant) explains that braces fell out of common use in the 50s, in part because of Hollywood. Brando famously appeared in jeans with a belt in The Wild One, and teenagers rebelled accordingly, casting off their braces.
Braces were necessary when trousers were wide, with high waists, because otherwise they fall down. In England, side adjusters were a compromise, in order to avoid the belt. When waists fell, braces were no longer necessary (arguments about how trousers should hang, aside).
Popular with skinheads in the 70s and revived in the 80s, as featured by Michael Douglas, braces became a fashion item even though they were no longer necessary, functionally speaking.
Whether you prefer belt or braces, just make sure that your trousers hang correctly and have the right shape and contours. And a word about belt and braces: there is no point to both so unless you are genuinely paranoid about your trousers, choose one or the other.