Why did the South introduce a ban on cotton exports in 1861?

In many ways cotton was as sought after a resource as oil is today. So the Confederates seized this opportunity. Confederates placed an embargo on cotton exports in the summer of 1861. In order to starve the world of cotton, in hopes this would help further their ambitions.

They hoped to put pressure on Britain and France, in particular, to recognise them diplomatically which would put pressure on the North. Their textile industries were heavily dependent on American raw cotton and the economies of e.g. Lancashire would suffer (and did suffer) very badly without their supplies. The intention was that they would offer to lift the embargo when the foreign governments recognised them. This would then allow them to trade more freely, and particularly, they hoped, by the materials (e.g. iron, weapons) they needed to win the war.

It failed. The French seriously considered extending diplomatic recognition, but the British refused and the French would not act without the British. Instead, failing to export cotton helped destroy the economy of the Confederacy and was one reason why they printed over $1 billion in paper money which led to enormous levels of inflation.