Behind Iran’s overtures to Washington lie pent-up pressures for change – from sanctions and internal dissent to regional turmoil – that are shaping a rare chance to end decades of hostility.

For new President Hassan Rouhani, speed is of the essence.

Sanctions are squeezing Iran’s oil exports, economic misery is palpable, Arab Spring contagion poses a persistent threat and involvement in Syria’s civil war is a drain on hard-pressed resources.

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