The National Atlantic Treaty Organization and its 30 member countries have been forced to grapple with the role they should play in the conflict.
US President Joe Biden said on Thursday that no US troops would be sent to Ukraine, which is not a member of NATO.
In a speech from the White House, Biden said that his forces are not going to fight in Europe.
Several Eastern European countries in the body called for consultations under NATO's Articles 4 on Thursday morning, as reports of increasing shelling, bombings, and casualties across Ukraine poured in.
The North Atlantic Treaty Organization was formed in 1949 to provide security against Soviet expansionism and to encourage European political integration after World War II.
NATO serves as a collective security system, whereby its member states agree to mutually defend any attack on a member party.
When the alliance was founded, it contained just 12 countries, but has doubled in size in the years since. The body now has two countries in North America and 28 European countries.
Not a member of NATO, Ukraine has been designated as one of the alliance's enhanced opportunity partners, a title granted to nonmember countries that have contributed to NATO-led operations and missions.
NATO and its members have no obligation to defend Ukraine against Russia.
As the conflict escalates, pleas for NATO assistance are growing louder.
On Thursday, a group of Eastern European countries, including Bulgaria, the Czech Republic, Latvia, Lithuania, Poland, Estonia, and Slovakia requested discussions under NATO.
The territorial integrity, political independence, or security of any of the parties can be threatened, according to the treaty.
It is not a guarantee that the alliance will take action, but it is a step in the right direction. The formal communications begin on behalf of the member.
The alliance talks about whether the threat exists and how to counter it. NATO uses consensus decision-making, meaning there is no voting. NATO's website says that consultations continue until a unanimous decision is reached.
NATO made preparations for further Russian violence against Ukraine as it responded to the invocation of Article 4 on Thursday.
According to the alliance's website, NATO had only triggered the article six times before Thursday.
In February 2020, Turkey invoked the article after Syrian government forces killed dozens of Turkish soldiers in an attack on opposition-held regions in northern Syria.
The other five times it was used.
NATO responded with military assistance to Turkey on two of those occasions, aiding the country with missile batteries to combat Syrian attacks in 2012 and providing aircraft and missile batteries along the Turkey-Iraq border in 2003
The member meeting resulted in stronger NATO efforts to defend the alliance after Poland used the tenet.
World leaders attended an emergency virtual NATO summit Friday morning. The meeting followed a NATO summit on Thursday where members discussed the situation in Ukraine.
NATO Secretary-General Jens Stoltenberg told journalists the alliance would continue to send weapons to Ukraine.
The decision marks the first time in seven decades that NATO has used its combat- ready response force as a defensive measure.
—NATO (@NATO) February 25, 2022
This is an historic moment and the first time NATO has used high readiness forces in a defense role.
The force includes land, air, sea, and special operations forces from the alliance's member nations. The force was activated Friday, though troops have not yet been deployed.
It was not clear how many troops would be activated. The forces won't go to Ukraine.
Biden has made clear that US troops are in Eastern Europe to bolster NATO member countries that are wary of Russian aggression.
Ukrainian President Volodymyr Zelensky thanked NATO for its help, but called on the alliance to do more.
We are alone in defending our country. Who is going to defend us? Zelensky said that he didn't see anyone who was ready to give Ukraine a guarantee of joining NATO. Everyone is afraid.