The number of people in the labour force has change quite a lot over the centuries, and the number of people gainfully employed has tracked that quite closely. Ie unemployment has been relatively low and stable. (Despite eg women joining the labour force en mass over the course of the 20th century, or all the baby boomers, etc.)
That suggest the null hypothesis that to a first approximation the number of jobs is determined by the number of workers available. More workers seem to somehow lead to more jobs. (Immigration changes the number of workers, yes. But that's about it.)
What kinds of jobs are growing? Are any groups underemployed?
Are standards of living increasing? For who?
> More workers seem to somehow lead to more jobs.
Imagine the US merged with Canada and Mexico. The number of jobs would probably go up until we reached a similar level of unemployment. Would everyone be better off? Is that what economic growth looks like?
That's an interesting question. You can look up the statistics online. Eg I imagine we have a lot more baristas these days, but fewer people making buggy whips than 200 years ago.
> Are any groups underemployed?
What do you mean by underemployed? As long as the unemployment rate isn't 0%, mathematics will tell you that you'll find some people who are 'underemployed', yes.
> Are standards of living increasing? For who?
Yes, living standards are increasing at the moment for most people around the globe. (Basically for anyone who's not living in a failed state like Cuba or North Korea, or in an active war zone.)
> Imagine the US merged with Canada and Mexico. The number of jobs would probably go up until we reached a similar level of unemployment.
All three countries already have both people and jobs before the merger. Right away, the combined unemployment rate would be a (weighted) average of the previous unemployment rates in these three areas.
Over time things might change, depending on what exactly what gets merged. If there's free migration between all three territories, GDP would go up a lot.
Unemployment would probably mostly stay the same as before, but details depend on whether the new merge entity would take its labour laws from Canada, the US or Mexico, and a million other details.
> Would everyone be better off?
Virtually everybody, yes. Obviously, with hundreds of millions of people involved, you'll find a few here and there who will be worse off for almost any policy you can think of.
