Russia invades Ukraine

After months of military buildup and brinkmanship, Russia launched an unprecedented assault on Ukraine.

Explosions rang through a number of Ukrainian cities, including the capital Kyiv, in a broad invasion that began before dawn on February 24.

Fighting continues to take place throughout the country, and so far the Ukrainian resistance has been able to hold Kyiv and many other key cities. Meanwhile, more than 2 million refugees have fled Ukraine to neighboring countries, according to the United Nations' refugee agency.

The United States, the European Union and other Western allies have been rolling out sanctions in response to Russia's actions. Many people around the world have also been rallying in support of Ukraine.

Russia has been tightening its military grip around Ukraine since last year, amassing tens of thousands of soldiers, as well as equipment and artillery, on its neighbor's doorstep. The escalation in the years-long conflict has triggered the greatest security crisis on the European continent since the Cold War, raising the specter of a dangerous showdown between Western powers and Moscow.

CNN