The largest group of European nations not in NATO are those that profess their neutrality. Including nations such as Austria, Ireland, and Switzerland, some have military neutrality enshrined in their constitutions, or because of previous dealings with the great powers.

Polish Prime Minister Donald Tusk said on Wednesday he had asked NATO to open consultations under Article 4 of the alliance's treaty after Poland shot down drones in its airspace following what he called a "large-scale provocation" by Russia.

Article 4 allows member states to start a formal discussion within the alliance about threats to their security. It does not commit the alliance to military action.

Military capability of Western alliance remains 'formidable' despite questions around untested 'mutual assistance' agreement as Trump pivots away from Europe

NATO launched an "Eastern Sentry" to bolster the defense of Europe's eastern flank following Russia's drone breach of Polish airspace.

NATO’s Baltic members sent a joint letter to the US Congress, asking for a key military financing initiative to be preserved after the Pentagon said it planned to cut funding for European nations bordering Russia.

The drone barrage forced Polish airports to close. Karol Nawrocki, the president, called it “an unprecedented moment in the history of NATO and Poland.” In a speech to parliament, Mr Tusk called for the “full mobilisation” of NATO members,

One of the key unanswered questions is whether the Russian drones were sent to Poland intentionally or not. Especially for Europeans on the eastern flank, the incident was an “attack”