When you look back on Iran's history, you see a pattern.
Iran as we know it emerged in the 1500s as a shi'a nation under the Safavid dynasty. It was pretty much stable (with a few Afghan problems) until the late 1700s under the .
From the late 1700s to the early 1900s, Iran got caught up with border wars with Russia and later on became a pawn in Russian vs. British interests in the Middle East (aka the Great Game), which weakened the regime. So for all that whittling away at a once-great Persian empire, the Iranians could blame the Russians and the British.
From the early 1900s - say, 1925 - the Qajar dynasty ended and the first Shah propped himself up. Unfortunately, World War II made Iran a major pipeline for the British and Soviets, and with that Shah's pro-German leanings, the Allies invaded in 1941 and installed the Shah's son () as a puppet. So again, the Iranians could blame the Russians and the Brits.
In 1953, a popularly elected prime minister was nationalizing the oil industry. The Brits encouraged the United States to depose the prime minister, which they did. This led to Pahlavi becoming a dictator, crushing political opposition for 25 years. So for that, the Iranians could now blame the Americans.
In 1978-79, the Ayatollah Khomenei led an uprising against the Shah, driving him out into the protection of his American patrons. One hostage situation later, a lot of bad blood builds up and remains there between the U.S. and Iran. Iranians could still blame the Americans for that.
In 1980, Saddam Hussien figures he could smash and grab Iranian territories to expand his rule and greater access to Gulf seaports. So he goes to war against Iran, 8 bloody years of it, even with Saddam using chemical weapons. Iranians could now add Saddam to the list of blame.
From the 1990s to 2005, Iran was able to focus on internal matters and improving their economy. On foreign matters, they had to deal with Saddam to their West and the Taliban to their East, with Russia and their breakaway Islamic states to the North. Times are hectic, but slowly reforms are being made, and quiet attempts at reconciliation with the West being made. But Sept. 11, 2001 happens, and in 2002 Bush comes out with his "Axis of Evil" speech putting Iran on the spot. Getting bunched together with Iraq (whom they hate) and North Korea (with whom they really didn't do a lot of business) doesn't do the moderates in Iran's government any favors. Equally harsh is that the United States stops their dealings with Iran, even after the successful team-up they made driving the Taliban out of Afghanistan. Slipping prestige and a hard-line reaction to Bush's bullying by the governing mullahs prevent moderates from running for elections in 2005 (either the moderates failed to get permission to run, or they refused to out of frustration). When a hard-line crazy guy Ahmadinejad became President, Iranians suffer under his poor rule (corruption, global embarrassment, etc.). However complex the whole mess is, Iranians could seriously blame Bush and his neocon cronys for inflaming the situation.
Now, it's 2009. basically calls a questionable election result too early and too eagerly for . Even though enough Iranians know among themselves there's no way Ahmad could have won all those provinces so handily, even with widespread reports of ballot box tampering and fraud. Now acting like a bullying teenager caught in a weak lie, Khamenei is threatening violence on anyone who dares question him, and starts acting in a very Shah-like manner with violent arrests, use of acid sprays, the works. Thing is, for all of Khamenei's rhetoric against the Brits, and the Americans, and Zionists and 'foreign interlopers', the Iranian people know that's not really true. There's no evidence the Brits or the Russians or the Americans tampered with the election. It wasn't BBC or Fox News rushing to proclaim Ahmadinejad the winner "by divine will" inside of an hour after the polls closed. This time, the Iranians have no one to blame but their own leaders. And that's why I think the protests are going to continue, because Khamenei is now the target of blame. The violence will get worse, which is the pity of it all, but it's not gonna stop until he's gone.