On 24 February 2022, Russia invaded Ukraine, starting the largest and deadliest war in Europe since World War II, in a major escalation of the existing war between the two countries that began when Russia attacked Ukraine in 2014. The fighting has caused hundreds of thousands of military casualties and tens of thousands of Ukrainian civilian casualties. As of May 2026, Russian troops occupy roughly 20% of Ukraine. From a population of 41 million, about 8 million Ukrainians have been internally displaced and 6–7 million have fled the country, creating Europe's largest refugee crisis since World War II.