MoM change with aggr

[Mazilinho]

Hello! I am having the following fields: Month, Values, and Region!

I need to display a KPI with the MoM change.

 I use this formula: 

=(Sum({$<[Month2]={"$(=(Max(Month2)))"}>} [KPI Value])-

sum({$<[Month2]={"$(=(AddMonths(Max(Month2), -1)))"}>} [KPI Value]))/sum({$<[Month2]={"$(=(AddMonths(Max(Month2), -1)))"}>} [KPI Value])

What i am trying to add is an if clause inside the formula, to calculate this MoM change when Region='USA' for example.

Can someone please help me with this? Thanks!