Announcing this week that British troops will leave Iraq by the middle of next year, Gordon Brown and the Prime Minister of Iraq, Nouri al-Maliki, spoke about "building a democracy for the future and defending it against terrorism". Yet, if the war in Iraq has proven anything, it is the utter ineffectiveness of using military power to counter terrorism.

US President-elect Barack Obama has also pledged to withdraw troops from Iraq and I warmly welcome moves in this direction. My fear, however, is that a key motivator behind this approach is the desire to bolster troop numbers in Afghanistan. While the original Taliban regime may have been ousted, the movement itself continues to threaten that country's future security.

Yet not only does an even more visible military presence further increase the risk of fuelling extremism, it also distracts attention and resources away from strategies far more likely to be effective at tackling terrorism. For example, there must be an immediate ceasing of air strikes on targets in Afghanistan and Pakistan, in preparation for more long term measures. These should include support for negotiations between all parties involved in the conflict, reform of humanitarian aid and reconstruction funding to prioritise Afghan organisations over foreign contractors, and investment in the kind of lasting aid that increases self-reliance, not least in sustainable agriculture initiatives, for example.

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In Afghanistan, women have played a key role de-escalating the violence, as they have in other conflict zones like the Balkans, Somalia and Northern Ireland. However, despite being a signatory to United Nations agreement to include women in preventing and resolving violence, Britain is reluctant to engage with what this means in practice – be it training significant numbers of police women or supporting their role in development and education.

This aversion means losing out on opportunities to deliver a powerful kind of "human security", based on addressing human needs and grievances that, if frustrated and ignored, may fuel violence.

Paul Rogers, Professor of Peace Studies at Bradford University, uses the term "liddism" to describe the current mindset. He defines this approach as "keeping the lid on things rather than acknowledging the underlying problems".

Britain's commitment to nuclear weapons, for example, stems from a belief that one day we may need to contain all kinds of unimaginable horrors and will require the ultimate in force to do so. Yet for most people the greatest threats they face are socio-economic and environmental.

The global economy has failed miserably to deliver global justice. Around one billion people in the world live fairly comfortably – the remaining five billion do not. As Archbishop Desmond Tutu explains, "the real threat to global peace is failing to recognise our interdependence", and we do this at our peril. As worldwide recession takes hold and the consequences of environmental crises like climate change are felt, many hundreds of millions of the world's poorest people will be marginalised even further.

History shows that when this happens, violent social movements can materialise, often provoking a repressive backlash in return. In other words, self-fulfiling cycles of violence are established, breeding terrorism rather than countering it.

In the pages of this newspaper Howard Jacobson has accused me of being complicit in terrorist atrocities. Why? Because I do not acknowledge that seeking to unravel complex grievances is the same as justifying violent action in pursuit of them.

Killing terrorists will not destroy terrorism and I argue, instead, that the answers are more complex, less reactionary and, ultimately, far more difficult. The only people to blame for terrorism are the terrorists themselves, and they must in all circumstances be held to account – be they individuals, established governments or insurgent groups.

This is only the beginning of the process. Increased international efforts to solve festering conflicts and strengthen failed states, development assistance, promoting democracy and equality, effective and equitable resource management, consensus building, multilateral activity and strengthening the UN apparatus all have a role to play too. Surely the war on terror will only ever be won when we replace a culture of fear with one of respect, engagement, vigilance and solidarity?

The writer is the leader of the Green Party in England and Wales and a Member of the European Parliament