TOP 10 across multiple tables?

Hi.

I want to show top 5 countries by sales but I don't how I can do this. This is my database design.



 I currently have achieved a matrix that shows all country-sales like this:

So, how could I show only top 5 countries by their sales?

I worked on another project where I used this function:

RANKX(
           ALLSELECTED(Table[Column]);
           [SumOfSmth];;
           0;
           Dense
)

but it was "to do a top" on one table, not across many tables

Thank you!