# Make a hash of regions, pointing to an array of states in each region.
# use qw() to quote words. 
# Use _ for spaces, replace with space when turning hash inside out.
my %regions = (
    southern => [ qw(
        Alabama
        Georgia 
        Tennessee
        West_Virginia
    ) ],
    western => [ qw(
        Oregon Washington California Idaho Montana
    )],
   # ...
);

# Turn %regions inside out.
my %states;           # Winds up with data like $states{Oregon} = western
foreach my $region (keys %regions) {
    foreach (@$regions{$region}) {    # Copy the state list
        s/_/ /g;    # replace _ with spaces.  West_Virginia becomes West Virginia
        $states{$_} = $region  # Store the state info.
    }
}