The answer is mainly hygiene. You have to remember that people in cities basically used to drink water enriched with shit and life expectancy was far lower. Improving this didn't start with John Snow, although he was tremendously important in taking hygiene to another level. Of course, it wasn't monocausal, and there were other factors, too. Technology mainly benefited only a small percentage of the population, as today (although most people use technology today, you still have a huge discrepancy between those with the massive data centres and those with their little computers at home).
The answer is mainly hygiene. You have to remember that people in cities basically used to drink water enriched with shit and life expectancy was far lower. Improving this didn't start with John Snow, although he was tremendously important in taking hygiene to another level. Of course, it wasn't monocausal, and there were other factors, too. Technology mainly benefited only a small percentage of the population, as today (although most people use technology today, you still have a huge discrepancy between those with the massive data centres and those with their little computers at home).