The Russian revolution began in 1917, but the Soviet Union posed a mortal threat until the mid-1980s. As for the Chinese revolution of 1949, it was only last month that the regime in Beijing was threatening to go nuclear over Taiwan.
We in the English-speaking world never give up hoping that the revolutionaries will suddenly see the advantages of peace, the rule of law and representative government. That may be because we think our own revolutions - the English revolution of the 1640s and the American revolution of the 1770s - followed that pattern.
Yet there was no more bellicose British government than Cromwell's. And the United States was scarcely a peaceful power as it expanded from sea to shining sea in the century after independence.
So it was pure pie in the sky to imagine that the Islamic Republic of Iran, founded in 1979, was just about to morph into a touchy-feely democracy. Yet people did. Only last year I had dinner in Washington with the son of the deposed shah. His country, he assured the assembled company, would soon make the transition to democracy. People were fed up with the ayatollahs and the mullahs.
The same kind of argument used to be made by neo-conservatives such as Richard Perle, the former chairman of the US Defence Policy Board, and Michael Ledeen of the American Enterprise Institute.
"In Iran," President Bush himself declared in a speech back in November 2003, "the demand for democracy is strong and broad." Dream on. Far from being on the brink of democracy, Iran is now on the brink of becoming the single biggest threat to democracy in the world.