Yes, I understand that's the question at hand. In the case of Korea, there is a good argument to be made that the entire country would have had the quality of life North Korea has if it were not for the intervention.

> by definition ussr did not even have communism

Yes, and neither did China, nor Cuba, nor Vietnam, etc, etc. At some point we end up with a "no true Scotsman" fallacy. In any case, the fear was of "the thing calling itself communism", not "theoretical platonic communism".

The fear, at least for people who actually thought about the matter, was based on the following facts:

1) Communism (as it was being practiced; I will assume this parenthetical henceforth) was incompatible with fundamental aspects of society that were considered important in the US. For a simple example, if you look at the Bill of Rights (first 10 amendments to the US constitution), the only right that was not being actively being violated in the countries that called themselves "communist" was the one granted by the Third Amendment. Well, except it _was_ being violated in the USSR in the early 20s. But generally 20th century nation-states have housed their own soldiers.

2) Communism was actively expansionist when it had the chance to be; see eastern Europe, the Korean peninsula.

3) Communism had as part of its doctrine the goal of fomenting revolutions in countries that were not yet communist.

4) There were communist parties in various countries, including the US, and some of their members (not all, yes) were actively involved in item #3.

5) There were various people in the US who were not members of the communist party but were clearly sympathetic to the idea of the communist party having more power or seizing power altogether. A number of these people were highly placed in the existing US government.

So at least in some quarters there was the perception of a plausible existential threat to the US as currently constituted (literally; throw out the Constitution and replace it with a totally different setup).

In addition to this, there was of course the usual fear of the other, the fear of the labor movement on the part of owners of capital, and so forth. In many cases these various reasons for fear were self-reinforcing.

> Both countries were allies in world war.

Yes. That doesn't always mean much on its own; the USSR and Germany were allies from 1939 to 1941.

> What was the need for a piss of contest between the two?

This is a question without a simple answer.

To some extent, in both cases, it was driven by domestic political considerations. It's a lot easier to maintain power if you keep telling people there are external enemies they need to worry about and hence shouldn't rock the domestic political boat too much. In the case of the USSR this was a quite explicit (and longstanding; it dates back to the 20s) policy of the Communist Party. In the US, I think it was a bit more opportunistic and not as organized.

Add to that concerns regarding the fate of allies, the pre-existing tensions I talk about below, and lots of stuff I am not thinking of right now and may not even know about...

> I would say ussr's involvement in cold war was caused by passive aggressive tactics began by USA.

The tension dates back way longer than that. There were quite a number of people in the US who fundamentally mistrusted the USSR for the reasons listed above, and that distrust went back to the original October Revolution. There were quite a number in the USSR, including in high government positions, who distrusted the US because of its participation in https://en.wikipedia.org/wiki/Allied_intervention_in_the_Rus... . There was tension over the UN declaration of human rights and its article 13. There was tension over the post-war division of Europe. I'm sure you're aware of the Soviet blockade of West Berlin and the ensuing Berlin Airlift; that situation was not precipitated by the US. The Korean War was not precipitated by the US.

Claiming that the US "began" the cold war in some sort of sole act of aggression involves some serious revision of history as far as I can tell.

> It was USA who first deployed nuclear weapons near Russian border.

Yes. The context was that the US was looking for a way to be able to defend western Europe from invasion by Warsaw Pact forces. There was no realistic way to match those in terms of actual troop numbers and materiel without deploying a _lot_ more troops to Europe than the US was willing to do (for various reasons, including cost), so nuclear deterrent was viewed as a way to provide the needed defensive capabilities.

I agree that it was an escalation of the nuclear situation. I don't know to what extent the fears of a Warsaw Pact invasion of West Germany (say) were justified. But given what had just happened on the Korean peninsula a few years earlier, they weren't entirely baseless. I won't claim the missile deployment in Turkey and Italy was the right call, but I have a hard time categorically saying it was the wrong call...

> When russia deployed in response in cuba, suddenly that was news

In the US, sure. The deployment in Turkey was sure news in the USSR. ;)

> Most americans didn't even know that it was their country that started it

Indeed.

> Just like they are doing it now in the name of terrorism

I think the fear of communism was a _lot_ more justified than the current fear of terrorism. In particular, communism was a _lot_ more successful both in terms of seizing power and in terms of gaining mindshare in countries where it was not yet in power. For example, I have yet to see a US government official saying it would be good if the US were run more like ISIS-controlled areas. There were quite a few saying that sort of thing about communism in the 40s.

Again, I won't claim the US response to the threat was perfect. But I think the threat was real, and did need a response.