> I thought it was "universal" because it was meant to replace all social welfare programs with a basic income..
No. Universal just means everyone gets it. In fact, the word "universal" is redundant in the term "universal basic income" because "basic income" is already an income that everybody receives. It forms a base upon which you can build further income.
Some people believe that basic income should replace existing welfare programs, but it doesn't have to. After we implement a high enough basic income, we certainly might discover that we don't need some of these other welfare programs anymore. But in my opinion, there's not really any reason to shut them down ahead of time.
> But what about it requires to be at the federal level?
It's hard to implement a basic income if you don't issue your own currency. Currency is issued at the federal level, so that makes it a natural choice.
If you tried to implement it at the local level, you'd probably have to raise taxes or something... or create some kind of local or alternative currency. It's not impossible, but it's certainly less efficient.
> Does that mean smaller governments can't have UBI?
In a way, yeah. You've got to have a stable currency in which to pay the basic income. The smaller the government, the harder it is to maintain a currency. Furthermore, the amount of the basic income is constrained by the productive capacity of the economy. There's a limit to how much spending the productive economy can absorb. So if your country has a very resource-rich economy, you might be able to get away with a higher basic income.
But it's a continuum. The most efficient basic income is probably a worldwide basic income. Since the United States controls the world's reserve currency, they could probably pay everyone in the world a basic income in dollars without causing inflation or anything. But a country like Mexico couldn't do something similar.