Start with the commercial differences.
Separate markets when they have materially different margins, fulfilment costs, languages, offers or budgets. A campaign structure should reflect those business differences. Creating a separate campaign for every country by default adds work without necessarily improving decisions.
Check whether each campaign can teach you anything.
Estimate what a plausible acquisition cost means for the number of conversions your budget could produce. If a country is likely to generate only a few useful actions, short term results may be too noisy to judge. A focused test in one or two markets can be more informative.
Group only where it makes sense.
Shared language alone is not enough. Check whether the same offer, landing page and target economics apply. If markets are grouped, review where the budget actually goes; one country can absorb most of the spend.
Decide what would justify expansion.
Agree the evidence you need before adding another market: usable conversion tracking, a working fulfilment process and a credible acquisition cost. Expansion should follow a business case rather than a desire to cover more of the map.
Every business has different economics. Use these questions to inform a focused plan, then judge it against your own results.
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