Your first EU sale usually feels like a win. Then finance asks why blended ROAS dropped 15% overnight, and nobody can explain it because half the revenue came in euros and the other half in dollars, and someone's Google Sheet is doing the conversion at whatever rate they grabbed last Tuesday. That's the real starting point for ecommerce analytics for a brand expanding from US to EU: your existing stack wasn't built for two currencies, two tax systems, and five marketplaces reporting on five different schedules.