Which scientific achievement led to increased life expectancy during the industrial revolution?

it would be the development of Vaccine

For example, Before vaccine was invented, many people in Europe died from small pox. Approximately, small pox alone took around 400,000 of European people each year. (to understand how bad it is, it's important to know that their total population at that time was so small compared to the current population)

The development of vaccine prevented European people during industrial revolution from infected from many type of illness that could easily harm them due to lack of knowledge to treat them.

b. the 200th birthday of the united states

frederick the great and the war of austrian succession. frederick william of brandenburg-prussia trained his son, frederick, to be a hardy soldier. he also declared himself king of bohemia, and maria theresa sent troops to retake bohemia. in august he led 80,000 of these men across the frontier into bohemia, his