I don't know if anyone else has already pointed this out, but I was able to add a root node by specifying

FOR XML EXPLICITY, ROOT('CustomersByRegion')

The code below generated fully formed XML:

select

1 as tag,

null as parent,

c.countryname as 'Country!1!name',

c.currency as 'Country!1!currency',

null as 'City!2!name',

null as 'Customer!3!id',

null as 'Customer!3!name',

null as 'Customer!3!phone'

from

countries c

union all

select

2 as tag,

1 as parent,

co.countryname,

co.currency,

ci.cityname,

null,

null,

null

from

cities ci

inner join

countries co

on

ci.countryID = co.countryid

union all

select

3 as tag,

2 as parent,

co.countryname as [name],

co.currency,

ci.cityname as [name],

cu.customernumber as [id],

cu.customername as [name],

cu.phone

from

customers cu

inner join

cities ci

on

cu.cityid = ci.cityid

inner join

countries co

on

ci.countryid = co.countryid

order by

'Country!1!name',

'City!2!name'

for xml explicit, root('CustomersByRegion')

John