There were nations who abolished slavery in the middle ages

And most of those were either ignored later on or revoked.

Priests and clergy who work for a church which condemns slavery

And only applied to certain groups.

When did the Republic of Venice reinstitute slavery?

Priests and clergy were religious men and the French Republic banned religion.

Because, you know, the French Republic were full of fucking insane people.

The Republic or Venice is a city-state.

1347, Poland abolished slavery. Period.

Do you know what a city state is?

Singapore is a city state

A sovereign nation synonymous with a city

http://www.author.paulinemontagna.com.au/slavebackground/italy4.html

And, even then, Venice was a hub for the Medieval Slave trade.

Yet still banned by an elected leader and an elected assembly. Therefore the consensus must have been that it was wrong

Also, Poland practiced serfdom, which, if you didn’t know, is also considered a form of slavery.

I'd bet the same feeling was present in medieval China, medieval Japan, etc when they also abolished slavery

Serfdom is not slavery

The societies that “banned” slavery in the medieval era were feudal societies that essentially had their own form of slavery being conducted in the form of permanently tying the peasantry to the fields for life, giving them little to no chance to actually do anything outside of being a serf.

After all, why import cheap labor when you have plenty of it right now in the form of serfs.

Also note that Finland, Norway, and Sweden did not have serfdom

Norway, Sweden, and Finland were far removed from the slave trade because they had no economic incentive to have it. Even then, their entire formation as nations is based entirely on the slave trade.

Hell, they even gave us the word “slave” by capturing so many Slavs and selling them that the words became synonymous with one another.

Sweden banned 1335

However, they didn’t practice it much themselves because they had no need for it.

https://en.wikipedia.org/wiki/Swedish_slave_trade

Denmark/Norway banned 1803

Also, no. Sweden did not abolish slavery entirely until 1847.

The trend being obvious, slavery was considered abhorrent even before the grandparents of the Confederacy were born

And, in fact, they engaged in the slave trade throughout the 1700’s.

Hence slavery being banned in several states in the early years

The trend was only becoming obvious until the 1830’s.

When the United Kingdom outright banned the institution entirely within its dominion.

Even then, many areas took decades and upwards of half a century to end it because, you know, *you don’t end a long-standing institution with the snap of a finger and expect everything to go by perfectly alright.*

1777, Vermont.
1787, Northwest Territory of Ohio, Indiana, Illinois, Michigan, Wisconsin.

Regions that weren’t agricultural regions to begin with.

Maine joined the US as a free state in 1820

Yeah, in compensation for Missouri being a slave state.

First, it doesn't matter if they are agricultural. That does not make slavery moral. Second, you've probably never been to the north but there's a shitload of farms there. A couple hundred years ago there was a shitload more farms

First, it does matter if they are agriculturally

Agricultural regions tend to have an actual reason to have slavery exist.