Enum of long values in C#

Why does this declaration,

public enum ECountry : long
{
    None,
    Canada,
    UnitedStates
}

require a cast for any of its values?

long ID = ECountry.Canada;
// Error Cannot implicitly convert type 'ECountry' to 'long'.
// An explicit conversion exists (are you missing a cast?)

And is there a way to get a long value directly from the enum, besides casting?

This would not work either, for example:

public enum ECountry : long
{
    None = 0L,
    Canada = 1L,
    UnitedStates=2L
}