Iran's nuclear agreement has created a political and geostrategic earthquake in the Middle East and beyond, including accelerating the reform movement within Iran and empowering democratic constituencies in the Islamic world.
Liberated from external containment and internal suppression, Iran could now help itself, the region and the wider Islamic world towards greater prosperity, stability, and a pluralistic future. And Afghanistan will immensely benefit from the restoration of Iran's role as a responsible and secure neighbour and power.
Afghanistan's landlocked geography has been compounded by its political isolation in the region. Among its seven neighbours, only its borders with Tajikistan remain relatively free of political tension.
However, its long borders with Pakistan are infested by active military and political hostility; while Afghanistan's ensuing relations with Turkmenistan, Uzbekistan, and China are clouded by passivity.
The landlocked country's main regional partner, India, is constrained by a disputed territory and Delhi's residual reluctance for broader engagement.
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Afghanistan's relations with its other important neighbour, Iran, have been overshadowed by Iran and Saudi Arabia's regional proxy rivalry, Western countries' containment of Iran, Tehran's ideologically driven foreign policy, and some anti-Persian-Afghan elite.
Convergence of interests
Over the past 14 years, the US and Iran struggled to isolate Afghanistan from their mutual confrontation, as both recognised a convergence of their interests in Afghanistan.
In fact, Iranian Foreign Minister Javad Zarif was instrumental in facilitating the 2001 Bonn agreement that gave birth to the current political order in Afghanistan. Tehran also quietly helped US Secretary of State John Kerry's other diplomatic achievement - the formation of the Afghan National Unity government in 2014.
With the nuclear agreement, Tehran and Washington should be able to transform their cold peace into active cooperation on the stabilisation and development of Afghanistan. It will be a mutually beneficial trilateral cooperation.
Kabul could combine the US and Iran's complementary powers and assets. And the US would finally find a reliable regional partner for its Afghan mission and thus reduce dependency on its dubious alley, Pakistan.
For Iran, a secure Afghanistan is key to the security of its eastern provinces and the gateway to Afghanistan's abundant natural resources. Geostrategic proximity to China and Central Asia also plays a crucial role in the regional security.
The third way
The long term implication of a rehabilitated Iran for political orientation and development of the two countries are more promising. Both Afghanistan and Iran have suffered from colonial powers, politicised Islam, unfriendly relations in their neighbourhood, and global political strife.
Despite sporadic attempts to eradicate Persian culture and heritage by a small but powerful members of Kabul's ruling class and Tehran's monopoly of Persian civilisation, contemporary Afghanistan remains an integral part and inheritor of Persian civilisation.
Alongside Pakistan, Iran and Afghanistan are the three countries that are Islamic republics. While Pakistan is sliding fast towards "Islamisation", Iran and Afghanistan are moving towards democratisation.
Unlike many other Muslim societies, Afghan and Iranian societies are the only two Muslim-majority societies that have lived under the combination of Islamists' reign and global powers' proxy battles. Neither Islamists' promise of heaven on earth, nor the West's pretence of democracy can capture their imagination.
There are growing indications that point towards the emergence of post-Islamism and secular constituencies in Afghanistan and Iran. The consolidation of democracy in Afghanistan and Iran will present the third choice to the rest of the Islamic world: neither the Islamists' repressive, sectarian and backward agendas; nor the autocratic secular regimes' oppressive rule and divisive ethnic politics.
Iran's nuclear agreement was also a victory for Iran's reformist and pragmatic leadership, which will further isolate the confrontational factions. This might set in motion Iran's reorientation from its sectarian and ideological identity to its core civilisational and cultural essence: from an anti-Western, Shia Iran to a Persian Iran.
A Persian Iran might prompt resentment; but it will not be a threat to its citizens or to the region. It will be driven by the celebration of beauty, diversity and life, not by idolising death and conquest.
A Persian Iran can also help Afghanistan recover its Persian identity and heritage. The colonial powers' disintegration of non-European lands not only created artificial political borders, they also partitioned the region's shared cultural heritage and identity.
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The Iranian plateau and Persian language were divided into different and isolated pockets. The Persian language, which was the lingua franca of the Indian subcontinent for centuries, has become the victim of the British Empire's cultural genocide, while in Central Asia, former Soviet Premier Joseph Stalin criminalised the use of the Persian language.
The emergence of two independent political entities, Iran and Afghanistan in mid-19th century gradually shaped two distinct cultural entities: a Persian Iran and a culturally confused Afghanistan.
Despite sporadic attempts to eradicate Persian culture and heritage by a small but powerful members of Kabul's ruling class and Tehran's monopoly of Persian civilisation, contemporary Afghanistan remains an integral part and inheritor of Persian civilisation and the home of many of Persia's great personalities such as Zoroaster, Avicenna, Rumi, Jami, Behzad, Imam Abu Hanifa, and Gawharsad.
Persian has always been the lingua franca of Afghanistan, including the Pashtun, who have contributed immensely to the development of Persian culture and language as symbolised by the great Pashtu poet, Rahman Baba who was both a Pashtu and a Persian poet. The western Afghan city of Herat could be dubbed as the Jerusalem of the Persian world.
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Afghanistan's restoration of its Persian identity will also have a positive geostrategic implication. Currently, Kabul is dominated by security and ideological threats that are emanated from its southern flank as well its dependency on Pakistan for transit.
Timur Shah Durrani, the second ruler of the Durrani Empire, moved his capital from Kandahar to Kabul in late 18th century, primarily to escape the treacherous politics of tribal chiefs. Unfortunately, Afghan President Ashraf Ghani and the UK are reversing that trend by taking Kabul into Pakistan's orbit and providing political space to the Taliban at the expense of national and democratic forces.
However, emerging social trends, new security threats and abundant economic opportunities will help Iran, Afghanistan and like-minded nations realise Maulana Jalaluddin Rumi's promise: "Once severed from the root, thirst for union with the source endures."
Davood Moradian is the director-general of the Afghan Institute for Strategic Studies and former chief of programmes in President Hamid Karzai's office and chief policy adviser to Afghanistan's Ministry of Foreign Affairs.
The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.