[
NATO is for "preventing invasions" about as much as bath salts are for your bath... Like, yeah, that's the idea on the label but that's not the point...
Also I... Think you're kind of confused because NATO was created by a few western countries and later dominated by the US and let's just say neither the US nor Canada are anywhere close to Russia, and most of the original treaty countries were never in any real risk of invasion by the USSR and didn't share any borders. In fact Canada and the US are about as far from Russia as they can be. Greece is in NATO too. I can assure you that absolutely nobody in Greece has ever seriously had the concern that Russia may invade us. NATO was a cold war invention of the US, the point of which was to create a "western bloc" to counter the USSR primarily and serve the foreign policy interests of the US more broadly. The USSR had its own "NATO" in response, the Warsaw pact.
As for the invading other countries part, how common do you think what you are describing is? Russia has not done something like what you are describing to anyone besides Ukraine for a long time, and what is often missed regarding Ukraine is that a big part of the conflict is essentially a civil irredentist conflict between ethnic groups within Ukraine, like the Chechen wars in Russia or the troubles in Ireland. You're making it seem like Russia just keeps invading neighboring countries and is trying to take over everyone when it's just not in a position to do that neither really intending to, barring a few specific long standing disputes involving Russian populations in other places and occasionally sending troops to other places at the request of allied countries, like in Syria. Russia tries to exert influence a lot but not typically by invading other places, it's just not something that common.
As for the NATO thing, both Greece and Turkey are in NATO. And yet Turkey disputes some Greek islands, and is also occupying part of Cyprus. You probably don't know it but a couple years ago many people were worried there would be some sort of incident between Greece and Turkey which could escalate to war, kind of similar to the current stand off in Ukraine. But neither Turkey nor Greece are concerned about a Russian invasion. So you have countries within NATO (supposedly to protect member states from invasions by Russia, right?) that are not threatened at all by Russia, and are instead primarily threatened by other countries within NATO. And obviously NATO did not freak out about any of this nearly as much as it's freaking out about a non-NATO country, where a large component of the issue is essentially a civil conflict between ethnic groups. Does any of this sound normal to you?
NATO was indeed a defensive pact to counter the threat (real or perceived) of Soviet advancement through Europe.
Many countries, including Greece, were bordered by Soviet satellite states, which were little more than puppet governments, backed by significant red army presence that never left after the Second World War (Yugoslavia was more independent though). The Greek civil war was arguably the first proxy war of the early Cold War, with the communists receiving support from Tito’s Yugoslavia, Bulgaria and Albania.
Communists during the Greek civil war received very little external support. Basically the only support there was was limited supply of weapons, as well as helping communist forces find shelter on the other side of the borders. They asked for more support but the USSR was not interested in giving it to them at that point. The main external agents involved in the conflict were the UK and later the US (fun fact, the Greek civil war was considered to have been one of the first times Napalm bombs were used, some people think it was the first but in fact they had seen limited use during late WWII). Yugoslavia wasn't "more independent", it was pretty much completely independent after a certain point. Yugoslavia was its own thing, as was Albania and Romania eventually. They were not USSR satellite states, and at some points even had pretty bad relations with the USSR. But you did touch on something important. The Greek government wasn't worried about a Russian invasion. It was more worried about INTERNAL conflicts with communists, and it wanted to align with the western bloc. Similarly, Spain for example had no borders with USSR aligned countries at all, but faced potential internal conflicts and wanted to take a side.
It’s easy to imagine since the Soviet Union collapsed, that NATO are the big bad in everything, but the Cold War was quite evenly matched,
It was most definitely not evenly matched. At no point did the USSR have remotely as much power as NATO. But what governments were worried about was mostly the internal threat. The entire idea was to keep communists away from power, since in many countries including Greece, they had pretty broad support (especially in Italy where they seemed very likely to win, which eventually led to Operation Gladio and similar operations).
Out of interest, what do you think of Turkish invasion of the North Cyprus? Was that a legitimate response to the coup?
It was an expected response, but not a legitimate response, as they ended up occupying a large part of Cyprus which they basically ethnically cleansed of its majority by forcing them out of their homes and replacing them with populations imported from Turkey, not to talk about the war crimes (although the other side also committed numerous). At the end of the day, they split an island nation which had never been split in history in two.
There was actually two invasions, the first captured a very small part of the island, they didn't like the terms in the negotiations so they invaded again (after the junta in Greece had collapsed) and captured about a third of it and created a Turkish Cypriot state, when they ostensibly were trying to protect the integrity and independence of Cyprus. But overall I consider both the Greek junta-Greek Cypriot EOKA-B and Turkey to be at fault for what happened.
Through it all NATO just didn't really care at all because the point was never to protect countries from external threats, it was to expand the reach of the western bloc and restrict communism. Similarly now the US cares about restricting Russia. But when Turkey invaded Cyprus, or when their puppet government ordered to coup Makarios, they didn't care. Like, seriously, why is the Donetsk/Crimea situation, a conflict between non-NATO countries so important for NATO but the invasion and occupation of Northern Cyprus, a conflict between 2 NATO countries and one that isn't technically in NATO isn't?
I frankly consider it ridiculous that there are such conflicts between NATO countries and yet we're supposed to take NATO seriously as a defensive mechanism. Like, Erdogan is disputing Aegean islands, is trying to reopen Varosha in Cyprus (which is currently a ghost town since it's on a "dead zone" following negotiations) and regularly violating Greek airspace. NATO doesn't do nearly enough to resolve the conflict and that's between NATO countries (tbh that's probably for the better because if they did they'd probably mess it up). France and the US simply use the conflict to make Greece buy weapons from them. On the one hand I understand they don't want to alienate Turkey. So why do they want to alienate Russia so bad?
Also, supposedly NATO can only operate if a NATO country has been attacked. But if that is the case, why was Yugoslavia bombed when no NATO countries were attacked? Kinda makes the mission statement look ridiculous.