What was the Soviet Union, exactly? Why does Putin seem to be missing it?

The dissolution of the Soviet Union, according to Russian President Vladimir Putin, was a "catastrophe." What was the Soviet Union, and what is Putin's true motivation?

"The fall of the Soviet Union was the greatest geopolitical calamity of the century," Vladimir Putin, who has presided over post-Soviet Russia for more than two decades, says.

The phrase, made in a 2005 address to the country, is frequently cited to support claims that Putin wants to revive the 20th-century union of 15 republics, or even the Tsarist Russian empire that came before it.

So, what was the Soviet Union — or, to give it its full name, the Union of Soviet Socialist Republics (USSR) — and why should Putin be saddened by its demise?

By land area, the Soviet Union was the world's largest country.

After the Russian Revolution of 1917 overthrew decades of tsarist tyranny, the organisation was created in 1922. After a brutal civil war in which 'White' Russians, backed for a time by the major European nations and the United States, set out to restore the monarchy, the Soviet Union was formed.

At originally, the union was made up of 12 republics. Russia was the most populous, followed by two other Slav republics, Ukraine and Belarus, Moldova, three Caucasus countries (Armenia, Azerbaijan, and Georgia), Kazakhstan, and four other Central Asian countries. Estonia, Latvia, and Lithuania, the three Baltic states, were seized in 1940.