US sales stable – where to expand next? UK, EU, Japan, Australia, Saudi?

Quick Vine note:
If you use the same ASIN in 10 marketplaces, you can technically get 30 Vine reviews in each – 300 total – and they all sync. But once your US listing is over 30 reviews, you can’t do Vine again *in the US*, but you can still do it everywhere else.
Some people make a separate ASIN in other marketplaces, run Vine, then merge it as a variant. That’s against Amazon’s rules though, so be careful.

Germany first, then UK, then Japan. Germany’s central location makes Pan-EU fulfillment really smooth. You just need VAT in Germany and maybe one other EU country. UK is big but has Brexit customs headaches.
Authorize from the US, but if you’re serious about Germany and UK, get local trademarks. It’s night and day for fighting hijackers.
Inactive sites are low-risk with vacation mode.
Vine works per marketplace, no issues.

I’d go Germany first, then UK, then Japan. Germany is the biggest in EU, and with Pan-EU you can cover a ton of countries with one VAT. Just be ready for all the compliance hoops.
You can authorize your US brand to EU, but without a local trademark, you can’t really fight hijackers properly. There’s also a big risk of someone squatting your brand in EU and then shaking you down for money. If you start moving units, register your brand there too.
Inactive marketplaces are usually fine if you just set vacation mode. Lots of sellers do that.
Vine works per marketplace, 100%.
Europe (Germany + UK) first, then Japan. EU volume is huge but a headache to set up. Japan is consistent but product-dependent. Australia and Saudi are only worth it if you have extra stock.
Brand authorization is the same across regions. Canada is usually auto-included with US, so you might not need to do anything extra there.
Opening markets and not selling can be risky. Most people either stick to vacation mode or only open what they’ll actually run.
Vine is per marketplace. A lot of sellers use this to stack international reviews that all sync back to the US listing.
One thing you didn’t mention – a lot of people expand *defensively* to keep hijackers from listing on other marketplaces and messing up the US ASIN with bad keywords. If you can’t run all of them, at least claim the ASIN in the big ones.

Europe is definitely the next biggest volume after North America, then Japan – which has been way stronger this year. Australia and Saudi are pretty small in comparison. Just make sure you check how your category performs in each region first.
For brand authorization, you can authorize your US brand to other marketplaces. Go to Brand Registry, open a case saying “Update role or add new user to account,” and put in the email and seller token for the other marketplace. That unlocks A+, Vine, stores – everything.
If you open a marketplace and just let it sit empty, you can get hit with a dormant account review. They’ll ask for credit card bills, ID, business license, stuff like that. If you fail it, it *can* spill over to your US account. To play it safe, put unused marketplaces in vacation mode and keep the balance at zero.
You can absolutely run Vine per marketplace. Even if reviews sync, the 30-review Vine limit is per marketplace. A lot of people launch the same ASIN everywhere and run Vine everywhere at once – all the reviews stick together.
EU (especially Germany, UK, France, Italy, Spain) has the biggest combined volume by far. But compliance is no joke – VAT, packaging laws, WEEE, all that. Japan is also solid, but you might need certifications depending on what you sell. Australia is pretty easy to start, but volume is low. Saudi has okay margins but tiny overall sales.
Don’t open marketplaces you don’t plan to actually run. Empty accounts trigger checks. If you really want them open, list a few FBM items cheap just to keep it active, or use vacation mode.
And yes, Vine is per marketplace. Reviews from other sites might sync, but they don’t count against the 30-review limit for Vine in that country.