If Turkey attacks Greece, which country (or countries) are most likely going to help Greece?
very simple actually
Forget NATO
Within the same alliance Turkey is strategically more important than Greece, no matter what. What saves Greece is the Greek American political lobby: even if the US executive backs Turkey, US Congress and Senate will always back Greece, particularly if the Jewish American lobby is also involved.
Mutual defense clause & the European dimension:
Eurozone member’s budgets need to be approved by Brussels, hence current talks of Greece upgrading/renewing its arsenal always stumble on EU’s financial orthodoxy. On the other hand, while other EU members are suspicious of France’s “colonial/military” ventures, the defense of EU borders has become the core of France’s willingness to lead European defense, something Berlin, Rome or Amsterdam cannot afford to refuse and which answers Poland’s and the Baltic States’ fears.
The Treaty of Lisbon strengthened the solidarity between EU countries in dealing with external threats by introducing a mutual defence clause (Article 42(7) of the Treaty on European Union). This clause provides that if an EU country is the victim of armed aggression on its territory, the other EU countries have an obligation to aid and assist it by all the means in their power, in accordance with Article 51 of the United Nations Charter.
This obligation of mutual defence is binding on all EU countries (except maybe Denmark and Sweden).
Now, with that said, why would Turkey want to pick up a fight with its major trading partner and its major source of foreign investment?
Furthermore an activation of a European defence will mean termination of NATO, which the US or Russia cant afford, since they encourage a weak and divided alliance.
Some people have funny ideas.