No it wasn’t, the issue of slavery didn’t even enter the picture until the third year of Lincoln’s war when he couldn’t get anybody to sign up to fight it, so he duped the north with the great emancipation proclamation that didn’t free one slave, AND exempted the five slave holding states in the north.
The secession was caused by over reach of federal government from issues stemming back before 1837...if you’d cracked a book and studied the history of it instead of just reading the secessionist documents, you would get the whole picture...but your mindset to blame the south won’t let you do that.
If the north had been serious about abolition, why did they elect a racist president? Why were five of their states still slave holders? Why was Massachusetts dependent on the Cabots who were slave shippers even up until 1900! You see the slaves only entered the problem when the south told them to take a hike and left their arse dangling with no money to fund their government coffers from all the tariffs from the ports that the south held. The north crashed their manufacturing when the unions (YES, UNIONS)priced themselves out of business and the south wouldn’t buy their products when they could import them cheaper.
In fact the north was full of nothing but hypocrites who decided since they couldn’t make it to strip the south of their slaves.
"Our position is thoroughly identified with the institution of slavery - the greatest material interest of the world."
By their own words, the secession was all about slavery.