An you make a logical guess how size might effect a nations willingness to grant citizenship

There could not be enough space within the nation for all
its residents and citizens.
I hope this helps!

The bigger, and more powerful a country is ( bigger referring to both size, political power, and economic strength), the more likely a country is to have a higher immigrant rate. this is due to the fact that 3rd world countries typically dont need an increasing labor pool, rather, they would need to focus on building a stronger government first.