From the article An Extra Session of Congress, it almost seems as though it was a deliberate provocation by the Pubbie CONgress, forcing Lincoln to act against his own will.
It cheesed off the Brits mightily - except a certain sewer rat living in Britain who has plagued the world and caused the death of millions, even after he checked out of this life:
"Communist philosopher Karl Marx was among the few writers in Britain who saw slavery as the major cause of the war."
A non-sewer rat wrote about his perception of the war:
The well known novelist Charles Dickens used his magazine, All the Year Round, to attack the new tariff. On December 28, 1861 Dickens published a lengthy article, believed to be written by Henry Morley, which blamed the American Civil War on the Morrill Tariff:
If it be not slavery, where lies the partition of the interests that has led at last to actual separation of the Southern from the Northern States? ...Every year, for some years back, this or that Southern state had declared that it would submit to this extortion only while it had not the strength for resistance.
With the election of Lincoln and an exclusive Northern party taking over the federal government, the time for withdrawal had arrived ...
The conflict is between semi-independent communities [in which] every feeling and interest [in the South] calls for political partition, and every pocket interest [in the North] calls for union ...
So the case stands, and under all the passion of the parties and the cries of battle lie the two chief moving causes of the struggle.
Union means so many millions a year lost to the South; secession means the loss of the same millions to the North. The love of money is the root of this, as of many other evils ... [T]he quarrel between the North and South is, as it stands, solely a fiscal quarrel.
Whig-Republicans had long favored higher protective tariffs.
Morrill-like upward revisions began to be submitted soon after the lower Tariff of 1857 passed.
Morrill's proposal came in 1859 during a Democrat administration & Congress -- it went nowhere.
So Morrill had nothing to do with secession, it was simply long-standing Whig-Republican policy which finally passed in early 1861 because Southern Democrats resigned from Congress.
On March 23, 1861 the New York Times saw high tariffs as an issue and so proposed Congress should adjust Morrill rates and, if necessary, "get tough" with Confederates.
Sounds very Trump-like to me.