/cries in an at-will state/
If your colleagues gets fired for some bs reason you and your other colleagues can stand for each other by striking.
That's because unions are an integral part of the way many of the countries socio-political systems work. In Norway, for instance, the trades unions and the employers get together once a year to hammer out what is called tarriflønn, essentially the going rate for each broad type of job. The state provides a referee for the meetings whose job is to keep them on track and to encourage both sides to compromise. Unions and companies work together rather than fight each other, most of the time.
But this can only work if there is a broad consensus that we are all in the same boat and that we will all be better off if we work together.
The attitude, that appears to be common, in the US that employers are always exploitative, employees are always lazy and thieving, that the government is just a parasite, and that the aphorism "Good enough for government work" is a synonym for delivering shoddy work means that no one trusts anyone so you end up fighting all the time.
On a side note, what happens to health insurance for employees who're let go? Does it end the time of your last day or midnight? I was too afraid to Google it as I likely knew it's be pretty cut throat, but have always stressed about it regardless.
Fire for cause means "you aren't doing your job properly."
Redundancy means "your job is no longer required."
If twitter restructures to save money, the jobs that no longer exist have been made redundant.
Maybe I misunderstood the point you were trying to make?
In US usage, the general term here is “layoff”. And severance is not a legal requirement, and practices vary considerably by industry and, within industries, by individual firm. Layoff is eligible for unemployment, while firing may or may not be. (The line is also looser because the US has at-will employment, so there are very little general rules–other than those in particular employment contracts of unionized or high-status employees–around termination other than for prohibited purposes, or–mostly around warning periods–mass terminations, but there are conditions for unemployment assistance.)