Marx and Lenin and Stalin, o my.

The predominant struggle of the last sixty years was that of democracy vs communism. The Cold War wasted untold billions on armaments, irrevocably damaged many countries, and has repercussions, largely accidental or careless, which we see today in Iraq, Pakistan, Afghanistan, Africa, Cuba, and countless other parts of the world.
Apart from a brief study of 'The Communist Manifesto' some six or seven years ago, I realised I knew little of how the other half lived, and thought, and dreamed. So I dug a little into communism and all those other -isms to see precisely how they worked, or rather if they worked.

The first thing to know is that 'communism' is an idealised end state, achieved after a long struggle, where communities maintain themselves in harmony; man did not exploit man, and all gave, and all had. This ideal was a dream that was never reached, and realistically never could be reached by any society of greater than perhaps 150 people for short periods. It was a system designed for saints, of whom, as the saying goes, there are few, whereas capitalism was designed for sinners, of whom there are many.
Marx (with credit also to Engels) penned his manifesto while seated in the very pink of capitalist privilege, the British Library. For Marx, the market was anarchy: it exploited and alienated people, and created unintended consequences. He was infuriated by the powerlessness of the worker (the proletariat) and the ascendancy of the business-owning middle class (the bourgeoisie [bor-zhwa-zee]). His belief was that workers, if given sufficient power, would create and maintain a more equitable society.
Jumping straight to communism is simply not possible. 'Socialism' is a transitory stage in which there is a 'dictatorship of the proletariat' whose job it is to distribute goods and services evenly. It is an economic system where production is nationalised. Thus one would have a socialist revolution with a view to eventually purifying society enough to advance to communism.
This was a time when it was pretty awful being anywhere in the bottom 90%. You and your children would work in a factory for 12-15 hours a day, tip your toilet into the street, lose most of your teeth by 40, and die upon having your fifth child. The idea of having a smidgen of power and freedom was more intoxicating than penny gin, though marginally more dangerous.
A vast swathe of Europe rose up and rushed about in 1948 and around that time; France much earlier (see Les Miserables) and Russia much later. Most of the revolutions were disorganised and extremely dangerous to be part of. England, true to form, trod slowly and carefully through a bloodless revolution, perhaps remembering how dull Cromwell's petit-revolution had been in the 17th century.
Russia's revolution came very late because Russia remained virtually medieval outside the major centers. It was only the spur of WW1, with its toppling of the old order of aristocratic Europe, that Russians got the idea into their heads to do the same. It helped that the post-war army was scattered all over the map; certainly a rag-tag bunch of intellectuals (i.e. people who wore spectacles) and torch-wielding shoeless peasants wouldn't have had much luck otherwise. With Lenin at their helm they killed as many rich people as they could find, and set up a little government.
Lenin headed the Russian socialist state from its formation in 1917 to 1922, when he got ill. Stalin took over and initiated his 'social fascism', which really got things moving. Russia got rather powerful, but this involved killing quite a few people (Lenin was more about disenfranchising and deporting; he killed only 6m vs. 30m, but he wasn't in power as long).
As I mentioned earlier, Russia was to a large part medieval at that time, so the changes pushed through five centuries' worth of technology in just a few decades. Large changes plus large population plus large country equals rapid power shifts, and Russia started taking over other countries.
The USSR was a totalitarian regime: it controlled not only currency and goods, but also the hearts and minds of its citizens. The ideology of purification, of cutting out the diseased elements of society, had no logical end in sight. Everyone was suspected; rules were capricious; law was total. Although the ostensible goal was to achieve communism, the practice merely served to cement Stalin's rule. Top-down orders trucked grain from fields in the east, leaving the farmers themselves starving. The socialist state failed to serve the workers, instead institutionalising the very inequality revolutionaries had fought against.
As with most totalitarian states, an inordinate amount was spent on great shows of force. By 1980 the Cold War arms race had left Russia virtually bankrupt. It had few natural resources and exports, and little food. It began cutting loose USSR satellites with all but Georgia gone by 1992.

Marx's original idea--to replace the free market with centralised order and direction--was flawed.
He believed that a seemingly chaotic system was rudderless and random, but this was not the case; a process of natural selection helps a free market evolve. Also, he did not consider that the new controllers would be untrustworthy, greedy, and corrupt (in short, human). A centralised system has more potential for abuse than a lasseiz-faire system, as when it fails consumers have nowhere else to turn. Government does not compete with itself. When it no longer serves the interests of the people, there must be checks and balances in place to correct it, and in the hastily-assembled socialist assembly there was little thought given to potential corruption. They were believers, and thought that their righteous fervour would serve.