Once upon a time, the standard unit of measurement was an Ugn. As in
Mrs. Neanderthal: How much mammoth did you bring home?
Joe Neanderthal: Ugn.
Lots of cultures tried their own measurement systems. The Egyptians tried the mummy hand and later the pyramid brick as the basis of measurement. The Greeks opted for the olive and then the laurel. The Italians tried various types of pasta. None of these (including the pasta that was thrown at the wall) stuck.
Royalty decided to get involved in the measurement game and (being Royalty) whatever they said was the way things got measured. Given the high turnover in the world of monarchs, measurement systems changed frequently.
In the 16th century, Simon Stevin came up with a decimal notation system and in the 17th century John Wilkins came up with a different decimal system. Pretty much everyone ignored them except Wilkins’ cat who didn’t really care about a decimal system but was quite attached to the idea of being fed.
Then came the French Revolution. Many people think the French Revolution had to do with lack of food, inequality, and the need for a new flag. In fact, the French Revolution had everything to do with a new way to count (this was the original New Math).
This was the era of Humanism (Pi studied that in World History which makes me an expert) which means that Humans Thought Things Up. In this case, humans based the system of measurement on the natural world: the meter (or metre as it was then known) was based on the dimensions of the earth, the kilogram was based on water volume, and the 2-litre was based on a reasonable unit of Caffeine Free Diet Coke.
In the United States, the standard unit of measurement continued to be Anything that Wasn’t Metric. As I understand it, chickens were quite a popular unit of measurement.
July 28, 1866 (you now know why I’m talking about this today), the metric system became a legal measurement system in the United States. Absolutely no one cared.
In the 1960s and 1970s, the metric system became very chic (and by “very chic” I mean everyone (and by “everyone” I mean school administrators and the government) was convinced that the metric system would take over the US and become the most only recognized unit of measurement in the country). This translated into a lot of extra homework and not much else, since (hindsight being what it is) we still pretty much ignore everything metric (except when it comes to bottled soda).
Give an inch, take a meter?