Create a new table from existing columns

Hi,
As a new power bi user im looking for some clarification on best practice approach on how to process the introduction of a new table im working with. The new table is summarised at a higher level than the new measures table im looking to introduce. so i cant see how a straight relationship will work.

The data sources
I already have an existing table which has a month, country and each country has a further 29 subcategories, plus a measures column.
the challenge is that i have a new table with month and country only (no subcategories) and its associated measure.
So im looking for advice on the best approach to introduce the new two-tier table to the three-tier table.

cheers
peter