Back then I assume the only way to cut a beard was with a straight blade--how did Jewish men shave?
Prior to the advent of "shaving powders" (and later electric shavers) the only permissible manner in which men could shave their beards was to use a very sharp pair of scissors as an ersatz shaver. This method was discussed in BT Nazir 40a and 58b.
When "shaving powder" (which chemically removes hair) became available, most poskim permitted its use as well.
This teshuva from Rabbi Dov Lizner includes a plethora of information on the topic: https://library.yctorah.org/lindenbaum/halakha-and-electric-shavers/