Boiling
Always keep in mind the four main variables of good laundering practice: time, *water* temperature, mechanical and chemical action. When you decrease one the others normally must increase to compensate. OTOH when one is increased the others can often decrease.
Boling laundry in the days before mechanical much less automatic washing machines lessened the amount of scrubbing, beating and other manual labour involved on wash day. Stains were pre-treated (such as it was), then items would soak in cool water with perhaps a bit of soda. Next things would be placed into whatever vessel (kitchen copper, boiling pot, etc...) filled with hot soapy water and then boiled for a period of time.
Boiling in soapy water allowed the soap and the action of high temperature to lift off much of the remaining soils/muck from textiles that hadn't been taken care of via soaking. While boiling is hard on fabrics it probably was less than repeated beating, scrubbing and so forth.
The other way of doing things was after soaking was to soap everything up first, then wash in water hot as hands could bear, get as much of that soap out then place in a boiling pot. The boiling acted to help open textile fibers so they would release any remaining soils but also all that soap (which is very difficult to remove) again without all that beating/manual mechanical action.
Then along came sodium perborate and Persil.
Europeans long avoided eau de Javel (chlorine bleach) for textiles fearing it would rot/damage fine fabrics. This is quite true when you consider historically linen and hemp made up a large portion of clothing such as undergarments, bed and table linens, shirts, etc... Cotton would not become widespread until after the North American colonies began exporting the stuff to Europe, and even then with the widespread use of slave labour. Ironically cotton was not unknown in old Europe. It had been brought back from Egypt and other Middle Eastern lands during and after the Crusades. But cotton will not grow in much of Western Europe, and it never occurred to anyone to simply bring back the fiber and spin threads at home.
Anyway, with the advent of perborate bleaching systems housewives could "soak, boil, rinse" and that was it for laundry day. Perborate bleaching systems require temps >140F to become active, and are even better at boil wash temps.
Thus when semi-automatic and later fully automatic washing machines began to appear in Europe they had to do boil washes. Miele amoung others created units that had could be fired by coal or wood for heating.
Women/households that could not afford washing machines (and many could not) went on boiling laundry on ranges or in coppers right up until really after WWII when Europe began to rebuild after the war, but things didn't really take off for most countries until really the 1960's when the "boom" that had been underway in the United States since the 1950's took hold in Europe. Households then started to splash out for "mod cons" including semi and fully automatic washing machines.
The final key to all this was various European countries having to rebuild their power grids after the war and making decisions as to voltage and amperage for domestic use. New construction of housing fully wired, and or the wiring of older homes also helped.
Washing machine manufacturers began to ramp down boil wash temps during the energy crisis of the 1970's. That event also coincided with the discovery of bleach activators (TAED in Euorpe, and NBOS in United States). These chemicals gave "boil wash" results at temps <180F and even allowed perborate bleaches to become active at 100F to 140F range.