There's a good essay chapter on this in James McPherson's recent essay collection, The War That Forged a Nation. It specifically tracks some Confederates trying to sell cotton to the British and failing to foster an alliance.

I'm not sure about wider European perception, but I'd wager their views contrasted between a demand for cotton and moral dismissal of slavery as a barbaric practice.

I'm interested to see if anyone else has recommendations for this.

Some European countries, namely the British, were still wanting to get at the south's cotton, and so were willing to support the south through trade. The British were even willing to try to run blockades up until 1963, when the Union Navy began to prove too much for the British to regularly get through.

The Union, in fact, almost brought the British into the war in 1862 after an incident known as the Trent affair, where Union navy officer Captain Wilkes stopped a British ship, the Trent, and seized two Confederate diplomats from the ship. Obviously, this did not sit well with the British, who demanded that the diplomats be freed.

On the other hand, there were complaints from within the Confederacy about a lack of support from Europe. For instance, Jefferson Davis fired off a complaint in 1863 about European powers not recognizing the Confederacy as a legitimate nation. This manifested itself, he claimed, by the fact that Europe's policies on open ports seemed to be doing the United States a great deal of good compared to the blockaded ports of the Confederacy.

The culmination of Britain's stance on the war came in 1863, when they allowed the Confederacy to begin to build ironclad ships within their harbors. However, in a letter to the Lord John Russell, American minister to Britain Charles Francis Adams notes that should those ships escape British harbors and head to America, Britain can no longer be considered a neutral party and must, then, participate in the war. In the end, the ironclad ships are seized by the British and never reach the hands of the Confederates, keeping the British out of the war.

With all this about Britain, other nations did not have the same view. For instance, of all groups, the Russians supported the Union, noting that the two had a special regard for each other. This, perhaps, was more because the other major European powers were already poised to threaten the Russians at the time, but the fact that any European power was willing to come out for the Union was more than helpful to their cause. In fact, the Russians came to visit New York City in 1863. While the event really had no consequences besides a formal ball, it is easy to suppose that the presence of a major foreign power would have caused some discomfort for Confederate officers.

I hope this helped a little in answering your questions.

Sources:

Horatio Wait, "The United States Navy Blockades the Confederacy" (1898).

Thomas Taylor, "Aboard a Blockade-Runner" (1896)

Charles Francis Adams, "The Trent Affair Has Almost Wrecked Us" (1862)

Charles Francis Adams, "This Is War" (1863)

Jefferson Davis Complains of Europe's Refusal to Recognize the Confederacy (1863).

Rick Beard, "The Russians Are Coming!" (2013) - Part of the New York Times' Disunion series.

You may be interested in Karl Marx' letter to Abraham Lincoln. It can be found on the Marxist Internet Archive.