Mexico, Argentina, Brazil, Venezuela (when you could actually vote) are also federations (and not the only ones). Brazil's population is 210M and Mexico 126M. They all have national identity cards which can be used for voting like the parent comment says.
If there was will in the US for a national ID, Congress and the powers that be could achieve this within a few years if they wanted.
If there was will in the US for a national ID, Congress and the powers that be could achieve this within a few years if they wanted.