Member states of the North Atlantic Treaty Organization are scrambling to invoke Article 4 of the alliance charter as war erupts in Europe.

While Russian troops continue to secure holdings in Ukraine, NATO member states Bulgaria, the Czech Republic, Estonia, Latvia, Lithuania, Poland, Romania and Slovakia have all demanded a general security consultation. The alliance’s Washington Treaty allows for the immediate defense of member states under Article 5, but threats outside of the coalition’s territory must be addressed by other means first. Ukraine, as a non-member, is simply not eligible for the alliance’s immediate aid.

Article 4, now being invoked to address Russian aggression, has been called on several times in history, according to NATO.