Employer-provided health care in particular arose because of FDR enacting wage caps during his reign and then not only allowing for employers to not count money paid for employees' health care to be subject to the cap, it was also not subject to income tax. It continues to this day because the tax deductibility remains for health insurance premiums through employer provided insurance but not for self-provided insurance unless you fall below a certain AGI.
Wages today would likely be scarcely different for most people as there are few union shops around. Unless you work in a union shop or in a field where there are a lot of union shops (and thus your nonunion employer would need to compete with union wages to attract employees), unions don't affect your wages.
Nearly all of the rest are current in force due to federal and to a lesser extent state laws and regs, but the initial origin of those laws and regs can be debated.
Unions initially started because you had a small number of (relatively) big employers in an area, sometimes just one, and people could not easily move to other areas. The balance of power was very much in the hands of the employer(s) and as we all know, power WILL be abused. Unions as well as antitrust legislation were the initial response to this. As was noted above, unions had varied effects, some good, some bad, and some indifferent. (The antitrust legislation was widely thought to have been ineffective.) Arguably the automobile did far more to help improve working conditions as with them, employees could very easily vote with their feet and leave an area with poor employers and go elsewhere to work for better ones. I suspect this is why unions really declined after WWII- people could get much of the positives simply by moving and making employers compete for employees, but not having to deal with the associated negatives of a union.
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