My rule of thumb with Google Ads is to separate everything as granularly as possible (and as makes sense of course) from the beginning.
– different countries – different time zones
– different lingo. for example Apartment in the US, Flat in the UK
– different competitors
You will in fact see the breakdown by the countries if combine all under one campaign, however, if you would need to make an adjustment to one of the territories (aside from the bid adjustment) you would need to extract it and recreate it separately. Might as well do it from the beginning.