There has never been a communist country in the world. Yes, you read that right.

Before you start counting the so-called communist countries like USSR and Mao’s China, let us first go through what Communism actually is.
All such schools of thought like Marxism, Socialism, Communism were essentially a by-product of the post-colonial era. Karl Marx, the well-known German philosopher — or rather an activist, and economist gave rise to a form of new economy theory known as Marxism.
His work revolved around the issue that as Europe transitioned from centralized monarchies to quasi-democratic capitalist economies, workers or the labor class was being exploited by those who owned the means of production. In simple words, if you were working in a farm or a factory as many at the time did, whoever owned the factory or the farm got more out of the worker than they are putting in. This created an inherent inequality, giving the owners(whom Marx called Bourgeoisie), power over the workers(proletariat).
The solution to fix this inequality according to Marxism, society must shift towards a model where the workers hold those powers instead, by collectively controlling the means of production. This is where Socialism and Communism come into play. According to Marx, Socialism is the precursor step before communism and the next logical step after Capitalism.
In socialism, a democratic state controls the means of production rather than private companies holding the ownership. So, instead of competing against each other as in the case of capitalism, in Socialism, they would work together for the collective good under the control of the state. This is already the case in capitalist countries up to some extent like government-funded schools through taxes and other institutions.
But why the claim?
Once the state controls all the means of production, the next step is complete collective ownership, i.e. Communism. Not just of production, but all aspects of society and economy, including private property. The idea of Communism is to establish a classless, moneyless, and stateless society where everyone works towards the same collective goal of being happy and free.
Every so-called communist country is actually a socialist country, with the state controlling employment and economy to some degree. Even the widely referred to as “Communist Russia” was actually called the Union of Soviet Socialist Republics. Many major economists and studies consider Socialism to be a precursor to communism, which is only possible once a state has enough control over the economy and society. But this total control is a major reason why socialist countries struggle to reach this ideal state of communism.

Corruption was unbridled in countries like the former USSR, Venezuela, Vietnam, and North Korea, largely due to people in power, abusing that power instead of using it to help the society they control. Also, Socialist ideals have seen incredible success in some countries like Sweden and Canada.
The ‘human hurdle’ of overcoming power, greed, and government is the biggest reason we have never seen a true communist country.