[BroJoeK]

DiogenesLamp: "The only answer that made sense to me was: 'Those people making money off of the spending.' "

In 1860 it was Democrats, Northern & Southern, who'd been making money off Federal spending for generations.
Dems ran the place, they were the Deep State swamp.
In 1861 for the first time ever outsiders took over the swamp, fired all the swamp critters and just like today drove Democrats berserk.
Southern Democrats went screaming & wailing "we-we-we" all the way home.
Northern Democrats looked around and, finding no allies for sympathy, grumpily complained about rascally Republicans taking over Dems usual Federal graft.

It wasn't necessarily true, just partisan politics.

[DiogenesLamp]

You keep focusing on the contemporaneous labels of "Democrat" and "Republican" without looking at the underlying behavior of the two groups. Republicans of that era believed in "mercantilism" which is a form of command economy. They believed in protectionism. They believed in liberal causes of the day. When they finished with the abolition of slavery, they picked up enfranchisement of women, then abortion, and on and on to all the other liberal causes of the era.

The Republicans were the liberals of the 19th century, and much of the 20th century.