Categories and sub categories

I've got a membership database with different countries and groups. So I've setup 2 objects one for countries one for groups and then connected them to a members object which holds all the info on each individual member.

But is there a way that I can restrict the groups shown to the country chosen. So for example when a Australian admin role adds/edits a member they only get to choose from the groups in Australia, then for a different country same thing that admin only sees the appropriate choices for that countries groups.

Presume I would start by making those country and group fields multiple choice but then I'm not sure where to go from there?

thanks Jonathan

How to Create Dynamic Dropdowns in Forms

https://support.knack.com/hc/en-us/articles/226589108-How-to-Create-Dynamic-Dropdowns-in-Forms

that's awesome, thank Tony very helpful

Here is a quick screen share of how you only show the choices connected to the user etc. 

https://take.ms/YOAom

had to make a second one the first one had no audio

https://take.ms/AHYrk