i believe the demand for cotton had been going down due to ramping up production in Egypt by the British at the time. this also being one of the reasons no one was vary eager to help the south as they didn't really need their cotton any more. stop trying to justify the civil war as anything besides a war over slavery that's what it was and no excuses and accusations of the north forcing the Souths had are going to fly.
It's the other way around; Egyptian cotton became popular due to the Union blockade. When the Civil War ended, Egyptian and Indian cotton were once again superseded by Southern cotton as they were not as well suited for the mechanical looms of the time, tanking the Egyptian economy and helping (along with various profligate expenditures such as wars in the Sudan and the Suez Canal) pave the way for a series of defaults that resulted in effective British control of the country by the end of the century. Indeed, the very biggest reason that the French and British were unwilling to help the South openly was actually, astonishingly enough, slavery. The British especially could not stomach that, in spite of private sympathies for anything that took the Americans down a notch, because abolitionists had already won decisively in that country. The French might have been able to tolerate it due to the fact that Napoleon III did have autocratic powers, but even he couldn't just cavalierly overrule the entire liberal wing of his nation, which similarly disdained slavery. Economically and politically, it would have made perfect sense for both nations to step in and at a bare minimum crush the Union blockade; indeed, the French were already in the neighborhood propping up a puppet king in Mexico, which the Confederacy was much more amenable to tolerate than the Union was. The reasons they couldn't do so were social.
Also, it's worth noting that the South alone wasn't the only part of the Union to undertake nullification as a principle; it was endemic to all of the states. New England came very close to acting in 1809 and 1814, but in both cases were preempted (the former by the repeal of the Embargo Act that sparked the debate, the latter by the end of the War of 1812). As recently as 1859, just two years prior, Wisconsin attempted unsuccessfully to nullify the Fugitive Slave Act at the judicial level, resulting in a Supreme Court decision that set the precedent that state courts could not overrule the federal courts or federal laws (Ableman v. Booth), and states like Pennsylvania had done the same as well - South Carolina, in fact,
explicitly stated that these attempts at state nullification of the federal government were part of the reason for its secession.
The States of Maine, New Hampshire, Vermont, Massachusetts, Connecticut, Rhode Island, New York, Pennsylvania, Illinois, Indiana, Michigan, Wisconsin and Iowa, have enacted laws which either nullify the Acts of Congress or render useless any attempt to execute them. In many of these States the fugitive is discharged from service or labor claimed, and in none of them has the State Government complied with the stipulation made in the Constitution. The State of New Jersey, at an early day, passed a law in conformity with her constitutional obligation; but the current of anti-slavery feeling has led her more recently to enact laws which render inoperative the remedies provided by her own law and by the laws of Congress. In the State of New York even the right of transit for a slave has been denied by her tribunals; and the States of Ohio and Iowa have refused to surrender to justice fugitives charged with murder, and with inciting servile insurrection in the State of Virginia. Thus the constituted compact has been deliberately broken and disregarded by the non-slaveholding States, and the consequence follows that South Carolina is released from her obligation.
In other words, states' rights only exist insofar as they preserve and enforce the institution of slavery; the rights of states undertaken to restrict the flow of slaves is not to be countenanced, and is to be taken as justification for secession. Nullification in and of itself was not adequate for the Civil War; it was slavery that made the difference between another Nullification Crisis and the Civil War.
EDIT: It would truly help if I were able to actually finish my sentences. Also, it seems the Catholics of France did support the Confederacy, so that was an error on my part that I've excised. >_<