The link between slavery / Abe Lincoln, the civil war and Manchester isn't well know but was significant.
The Confederacy hoped that distress in the European cotton manufacturing areas (similar hardships occurred in France), together with distaste in European ruling circles for Yankee democracy would lead to European intervention to force the Union to make peace on the basis of accepting secession of the Confederacy. (The Union forces nearly provoked Great Britain to enter the war on the secessionist side, when its forces boarded the RMS Trent sailing under the British flag.  ) However, after Union forces had repulsed a Confederate incursion at the Battle of Antietam in September 1862, Lincoln issued his Emancipation Proclamation. Slavery had been abolished in the British Empire in 1833 several decades earlier after a long campaign. The Unionists believed that all the British public, would now see this as an antislavery issue rather than an anti-protectionism issue, and would pressure its government not to intervene in any way that helped the South.
Many mill owners and workers resented the blockade and continued to see the war as an issue of tariffs against free trade. Attempts were made to run the blockade, by ships from Liverpool, London and New York. 71,751 bales of American cotton reached Liverpool in 1862.  Confederate flags were flown in many cotton towns.
On 31 December 1862, a meeting of cotton workers at the Free Trade Hall in Manchester, despite their increasing hardship, resolved to support the Union in its fight against slavery. An extract from the letter they wrote in the name of the Working People of Manchester to His Excellency Abraham Lincoln, President of the United States of America says:
... the vast progress which you have made in the short space of twenty months fills us with hope that every stain on your freedom will shortly be removed, and that the erasure of that foul blot on civilisation and Christianity – chattel slavery – during your presidency, will cause the name of Abraham Lincoln to be honoured and revered by posterity. We are certain that such a glorious consummation will cement Great Britain and the United States in close and enduring regards. —Public Meeting, Free Trade Hall, Manchester, 31 December 1862.
On 19 January 1863, Abraham Lincoln sent an address thanking the cotton workers of Lancashire for their support. He wrote:
... I know and deeply deplore the sufferings which the working people of Manchester and in all Europe are called to endure in this crisis. It has been often and studiously represented that the attempt to overthrow this Government which was built on the foundation of human rights, and to substitute for it one which should rest exclusively on the basis of slavery, was unlikely to obtain the favour of Europe.
Through the action of disloyal citizens, the working people of Europe have been subjected to a severe trial for the purpose of forcing their sanction to that attempt. Under the circumstances I cannot but regard your decisive utterances on the question as an instance of sublime Christian heroism which has not been surpassed in any age or in any country. It is indeed an energetic and re-inspiring assurance of the inherent truth and of the ultimate and universal triumph of justice, humanity and freedom. I hail this interchange of sentiments, therefore, as an augury that, whatever else may happen, whatever misfortune may befall your country or my own, the peace and friendship which now exists between the two nations will be, as it shall be my desire to make them, perpetual. —Abraham Lincoln, 19 January 1863
A monument in Brazenose Street, Lincoln Square, Manchester, commemorates the events and reproduces portions of both documents.  The Abraham Lincoln statue by George Grey Barnard, 1919, was formerly located in the gardens at Platt Hall in Rusholme. The statue of Abraham Lincolnin Manchester, England
The Federal American government sent a gift of food to the people of Lancashire. The first consignment was sent aboard the George Griswold. Other ships were the Hope and Achilles.  To celebrate the aid a carnival procession was organised, carrying the bread for distribution from St Peters Square. The crowd first joined the celebration, but realising that this was a political stunt, stopped the procession and distributed the aid there.