Barely an hour after the first US and Israeli missiles struck Iran, President Donald Trump made clear he hoped for regime change. "Now is the time to seize control of your destiny," he told the Iranian people in a video. "This is the moment for action. Do not let it pass." Doesn't sound complicated. After all, with Iran's fundamentally unpopular government weakened by fierce airstrikes, some of its top leaders dead or missing and Washington signalling support, how hard could it be to overthrow a repressive regime? Possibly very hard. So says history. Washington has a long, complicated past when it comes to regime change. There was Vietnam in the 1960s and 70s, and Panama in 1989. There was Nicaragua in the 1980s, Iraq and Afghanistan in the years after 9/11, and Venezuela just weeks ago. There was also Iran. In 1953, the CIA helped engineer a coup that toppled Iran's democratically elected leader and gave near-absolute power to Shah Mohammad Reza Pahlavi. But as with the shah, who