US President Joe Biden met with the leaders of NATO's eastern wing on Wednesday, where he said democracy and freedom are at risk as Ukraine faces Russian aggression. 

"You are the first line of our collective defense and you know better than anyone what is at stake in this conflict. Not just for Ukraine, but for the freedom of democracies across Europe and around the world," Biden said. 

"Article 5 is a sacred commitment that the United States has made. We will defend literally every palm of NATO, every palm of NATO," he added. 

About Article 5: It is the principle that an attack on one NATO member is an attack on all members. It has been a cornerstone of the 30-member alliance since it was founded in 1949 as a counterweight to the Soviet Union.