Jeremy Corbyn’s landslide win in the Labour Party elections last month was a shock to the system of many in the political establishment on both sides of the Atlantic. Former Labour Prime Minister Tony Blair warned the party that it risked obscurity on a permanent basis if Corbyn won, yet Labour’s membership which spiked right before the leadership vote opted overwhelmingly for arguably the most left-wing major party leader Britain has ever seen.

Across the Atlantic at the very same time Corbyn was defying expectations, Bernie Sanders was beginning to pass Hillary Clinton in some New Hampshire public opinion polls sending off alarm bells inside the Democratic Party establishment. The political class which is always looking for explanations still hasn’t taken some of the lessons of the 2006 and 2008 elections to heart or the decline in liberal enthusiasm for the Labour Party in Britain to hear either.

It’s the Iraq War stupid.

For whatever reason the elite chattering classes inside the beltway and in the mainstream media have failed to recognize the impact of the Iraq War on the psyche and thoughts of those on the left. While academic studies and lots of ink had been spent talking about the political impact of World War II and Vietnam on the nation, the Iraq War which was fought in an era without a draft and initiated in large measure thanks to the complicity of the Democratic establishment and mainstream press is hardly seen as a factor in the shifting political landscape. But it was the defining event for a generation on the left in both the United States and United Kingdom.

Senator Hillary Clinton’s support for the “preemptive” Invasion of Iraq which mirrored that of Joe Biden and John Kerry’s continues to cast a shadow over her Presidential ambitions below the surface. Certainly not all Democrats were on board as the Iraq War vote loomed – our own Senator Bob Graham voted no while former Vice President Al Gore gave a scathing critique just weeks before the Congress authorized the invasion. But by and large those with Presidential aspirations voted yes on the war, recalling how the 1991 vote against the Gulf War had (according to political insiders) ended the serious Presidential aspirations of Georgia’s moderate Democratic Senator Sam Nunn. The theory was Nunn not Bill Clinton would have defeated George Bush in November 1992, had he not opposed what turned out to be a highly popular war which yielded an easy victory for the US-led coalition.

Of course history played out differently. Voting or supporting the Iraq War became a noose around the neck of so many politicians in the Democratic Party, and the war stimulated a whole new generation of liberal activists. The war also defined the left’s views about the world, some of which despite having opposed the war from before its conception I simply cannot agree with.

But this leads us back to Sanders and Corbyn. The popularity of “Democratic Socialism,” and some degree of liberal white guilt in a broader sense can be traced back largely to the fallout from a bungled war of choice. In the United States without a draft, the war disproportionately impacted lower-income and minority families. In the United Kingdom, it reinforced a notion on the left that the once proud nation that ruled the seas and half world had become a puppet state to the corporate driven capitalist ideology of its American cousin. The world view that faults the American elite and the west for problems across the globe largely grew out of the Iraq debacle. The activism and energy on the left that drives Democratic conversations and ultimately electoral victories also grew out of the war. The Sanders juggernaut is a logical outgrowth of this.

In the United States, the left looks to those like Bernie Sanders who advocate for a more compassionate and caring society while not engaging in a foreign policy dictated by corporate concerns, defense contractors who contribute to campaigns and hubris. Ultimately the attempts by President Obama and British Prime Minister David Cameron (a conservative) to initiate an Anglo-American military intervention in Syria two years ago was rebuffed. For the past 16 months, both leaders are grappling with fighting ISIS without having to commit large numbers of troops. The bottom line is the appetite for military adventurism has diminished greatly on both sides of the Atlantic thanks to the Iraq War and that the left outside of political insiders and Obamacrats do not fully trust this administration to keep the US out of a dangerous military conflict. Again, this fuels the Sanders phenomena.

In the United Kingdom, Corbyn’s ideology which is a mixture of outright social liberalism, what Americans would term as “radical” environmentalism and strong anti-Americanism on foreign policy (which includes being pro-Palestinian and sympathetic to the grievances of Arab countries against Israel), is a direct rebuttal of the Tony Blair leadership of both the Labour Party and the United Kingdom in general. Since the Iraq War was initiated, the left in the UK has become reflexively anti-American in the same way the right in the US was obsessively anti-communist during the Cold War. It’s actually not that dissimilar to the type of rhetoric the right led by Fox News uses in the US today to overstate the threat from anything related to Islam – the left in Britain now connects anything American (including the ownership of soccer teams by US businessmen) as against the national interests of the UK, and undermining of the national identity and sovereignty. It is worth noting that unlike in the United States where a “rally around the flag” effect took place after the Invasion of Iraq, the war was never popular in the UK.

Polarization the new normal is western politics. No event for the current generation of activists on both side of the Atlantic mattered as much as Iraq. Still, for some reason the chattering classes seem to forget the war as if it was just a blip on the radar – but that’s the wrong attitude.  The Iraq War was the defining political event of a generation.