Master Data Services :: Preventing Duplicate Inserts

In my trivial example below I have a Nationality entity. The entity just has the code and Name attributes, with the code being an automatically generated Integer. I am inserting one record and then trying to prevent the same record being inserted, by setting the ImportType to 1:

truncate table [stg].[Nationality_1_Leaf]
insert into [stg].[Nationality_1_Leaf](importType, ImportStatus_id, BatchTag, Name)
values(1, 0, 'some batch' , 'American' )
select * From [stg].[Nationality_1_Leaf]
exec stg.udp_Nationality_1_Leaf 'VERSION_1', 1, 'some batch'

After this I truncate the staging table and repeat the process. Unfortunately a new record is entered into the Entity even though the name is identical to a record that already exists.