I don't have a post for this, but also as a testament to China's poverty alleviation campaigns, world poverty is increasing if we exclude China.

When they write the history of the early 21st century, China's uplifting of millions of people out of poverty will be one of humanity's greatest acheivements.

Wrong, from the link I posted:

Capitalist hegemony has short-circuited people into buying wildly illogical and ridiculous propaganda like: "Lift yourselves up by the bootstraps" (which shows the almost religious power of capitalist propaganda, that the impossible can become possible), or "Communism doesn't work", when in fact Communism did work extremely well.

Examples from this post by /u/bayarea415, Stephen Gowans - Do publicly owned, planned economies work, Ian Goodrum - Socialism vs Capitalism and quality of life, and yogthos's USSR acheivements post about the USSR specifically:

• USSR had a more nutritious diet than the US, according to the CIA. Calories consumed surpassed the US. source. Ended famines.
• Productive forces were not organized for capital gain and private enrichment; public ownership of the means of production supplanted private ownership. It was illegal to hire others and accumulate personal wealth from their labor.
• Had the 2nd fastest growing economy of the 20th century after Japan. The USSR started out at the same level of economic development and population as Brazil in 1920, which makes comparisons to the US, an already industrialized country by the 1920s, even more spectacular.
• Free Universal Health care, and most doctors per capita in the world. 42 doctors per 10k population, vs 24 in Denmark and Sweden, 19 in US.
• Had near zero unemployment, continuous economic growth for 70 straight years. The "continuous" part should make sense – the USSR was a planned, non-market economy, so market crashes á la capitalism were pretty much impossible.
• USSR moved from 58.5-hour workweeks to 41.6 hour workweeks (-0.36 h/yr) between 1913 and 1960
• USSR averaged 22 days of paid leave in 1986 while USA averaged 7.6 in 1996., 2
• In 1987, people in the USSR could retire with pension at 55 (female) and 60 (male) while receiving 50% of their wages at a at minimum. Meanwhile, in USA the average retirement age was 62-67.
• All education, including university level, free. 2
• 99% literacy.
• Saved the world from Fascism, Taking on the majority of Nazi divisions, and killing 90% of Nazi soldiers. Bore the enormous cost of blood and pain in WW2 (25M dead), with the bloodiest battles in the history of warfare.. An estimated 70% of Soviet housing was destroyed by Nazi invasion. Nazis were in retreat after the battle of Stalingrad in 1942, a full 2 years before the US landed troops in normandy.
• Doubled life expectancy. Eliminated poverty.
• Combatted sex inequality. Equal wages for men and women mandated by law, but sex inequality, although not as pronounced as under capitalism, was perpetuated in social roles. Very important lesson to learn.
• Combatted Racial inequality.
• Feudalism to space travel in 40 years. First satellite, rocket, space walk, woman, man, animal, space station, moon and mars probes.
• Soviet power production per capita in 1990 was more than the EU, Great Britain, or China's in 2014.
• Housing was socialized by localized community organizations, and there was virtually no homelessness. Houses were often shared by two families throughout the 20s and 30s – so unlike capitalism, there were no empty houses, but the houses were very full. In the 40s there was the war, and in the 50s there were a number of orphans from the war. The mass housing projects began in the 60s, they were completed in the 70s, and by the 70s, there were homeless people, but they often had genuine issues with mental health.
• 66% of Russians polled in 2015 want the USSR back. The story is the same for all the former eastern-bloc countries: 72% of Hungarians say their country is worse off now than under communism, 57% of East Germans, 63% of Romanians, 77% of Czechs, 81% of Serbs (for Yugoslavia), 70% of Ukrainians, 60% of Bulgarians.

When it is claimed that a system works, we should ask, who it works for. Capitalism benefits a tiny number of rapacious capitalists, to the detriment of the rest of us, while Socialism works for the masses.

For an overview of the soviet experiment, watch this brilliant talk by Micheal Parenti, or read his article, Left anticommunism, the unkindest cut.

Also read this great article by Stephen Gowans, Do publicly owned, planned economies work?. Audio on youtube

Bonus vid about cyber-communism: Paul Cockshott - Going beyond money.

More sources: Socialism Crash Course, Socialism FAQ, Glossary.