Russia’s dependence on oil and gas revenues has long been one of the country’s greatest economic strengths. That same dependence is now becoming one of its most significant vulnerabilities. In November, Russia’s energy revenues fell sharply, underscoring how sanctions, weak crude prices, and currency dynamics are converging to squeeze Moscow’s finances at a time of elevated military spending. According to recent estimates, Russia is expected to collect roughly 520 billion rubles—about $6.6 billion—from oil and…