"Chandler was correct in his understanding that nothing would remove the cancer of slavery but bloodshed"
He meant the bloodshed of Southern American citizens, which is a direct threat. If you acknowledge his correctness, then you have to accept what he said was a threat.
Upon secession, slavery no longer existed in the Union, except in a few border states.
So, the 'cancer' had been removed, for the abolitionists, there was no need to spill Southern blood.
Then that begs the question of why Lincoln, i.e. the Republican Party, started the War.
With slavery gone, there was only one reason for war....stopping the free South from trading directly with Europe, and freeing the Mississippi to international trade.
Lincoln did not "start" the war but did act to preserve the Union and the Constitution from insurrectionists just as the document empowered him to do.
Presidents take an oath to preserve, protect and defend the Constitution and Lincoln fulfilled that oath. In so doing he became a figure of towering stature and took his place among the Immortals mankind will always admire for his courage.