The correct answer to this open question is the following.
The Emancipation Proclamation helped lead to the failure of cotton diplomacy because President Abraham Lincoln's Emancipation Proclamation ordered to free slaves in the Southern states. The proclamation granted freedom to all the slaves that worked in the large southern plantations in the case the Union Army won the Civil War. We have to remind that the Southern states depended so much on slavery to produce the cash crops that were exported to Europe.
So the cotton diplomacy or king cotton diplomacy was the strategy the southern states launched to restrain the exportation of cotton to Europe with the idea that this decision upset the European leaders and could support the Confederates in the Civil War.
The Proclamation was made on January 1, 1863.