Struggle against Islamist ideology will last centuries

It is often said that when the United States and its allies and partners topple a dictator like Saddam Hussein, they create a power vacuum conducive to the rise of militant groups, while also fuelling revitalised radical jihadist recruitment drives.

There is admittedly a historical connection between the collapse of Saddam's Ba'athist rule in 2003 and Islamic State's murderous blitzkrieg across western Iraq in 2014. Equally, George W. Bush's ill-fated invasion of Iraq no doubt provided talking points for fundamentalist imams.

However, the claim that international interventions are to blame for Islamism's rise masks an uncomfortable truth: Islamist gains in Iraq, Syria, Egypt, Libya, Tunisia and beyond would have been impossible without Islamism's popular appeal.

As the international community now recognises in the case of Iraq and Syria, there is an overwhelming moral obligation and a compelling strategic rationale to protect civilians and religious minorities against especially bloodthirsty forms of Islamist rule.

But we must also appreciate the limitations of external efforts to combat violent strains of Islamism.

When the ideology of Islamism enjoys widespread popular support, the hateful and sometimes genocidal terrorist groups that it spawns cannot be defeated simply by arresting their financiers, degrading their military capabilities, and killing their commanders.

Rather, ensuring that more Abdul Numan Haiders and Herve Gourdels are not casualties of the twenty-first century's war of religion will depend on winning a battle for hearts and minds against the ideology of Islamism.