NATO member states Poland, Estonia, Latvia and Lithuania have triggered NATO Article 4 to launch consultations within the alliance over Russia's attack on Ukraine.
“The Parties will consult together whenever, in the opinion of any of them, the territorial integrity, political independence or security of any of the Parties is threatened,” Article 4 of The North Atlantic Treaty says.
According to the NATO website, consultation under Article 4 can lead to collective action among the 30 member states.
The website says Article 4 has been invoked six times previously since the alliance formed in 1949, most recently by Turkey in February 2020 after dozens of Turkish soldiers were killed by an attack by Syrian government forces in opposition-held areas of northern Syria.
Turkey has invoked Article 4 on four other occasions: once in 2015 to inform the alliance of its response to terrorist attacks in the country; twice in 2012 after a Turkish warplane was shot down in northern Syria and after Turkish civilians were killed by Syrian shelling; and in 2003 when it asked for alliance help to protect its population from any spillover from the war in neighboring Iraq.
On two of those occasions, NATO responded with military aid, sending Patriot missile batteries to protect against Syrian attacks in 2012 and sending aircraft and missile batteries to southeastern Turkey along the border with Iraq in 2003.
Poland invoked Article 4 in 2014 after previous Russian aggression in Ukraine, a meeting that resulted in further alliance efforts to stand together against any threats.
Article 4 is separate from Article 5, which is the alliance’s declaration that an attack against one member is considered an attack against all.