is there a way to limit the number of non war attacks against countries without a tag? like for instance limit the land grabs on an untagged country to 5 in a 24 hour period? maybe that would help keep new players around longer.

It would help keep new players around longer on the alliance server yes - but the problem really is that the alliance server is heavily advertised as players requiring an alliance to play in

So in essence, the game itself promotes having less untagged countries.

The suggestion would also not work well: it will result in countries spamming the "attack button" as fast as they can click just before an untagged country exits the 5th attack protection, and the lottery will pick who gets the one and only hit in before it re-enters 5-hit protection.

would also prevent alliances getting land back from suiciders

suiciders are rarely farmed before they self delete or are killed anyway. I personally have a tag, always have and always will, but I noticed people coming back to the game just to be ran off by people farming them to death before they get a chance to join a tag