in the mid 1800s notherners used the term slave power to criticize what they believed to be the excessive political influence of which groups of people?

Southern slave owners.

Explanation:

Slave power was a concept developed by the abolitionists of the northern United States during the first half of the 1800s, to refer to the political and economic capacity that the large landowners of the south had in American politics, based eminently on agricultural production through the use of slave labor. Through this system of production, the most powerful families in the south increased their profits against the personal work of the citizens of the north.

At the same time, thanks to clauses such as the Three Fifth Clause established in the Constitution, slave states had an excessive representation in the House of Representatives, which was an obstacle for the political projects of the North that entered Congress as well as a way of exerting political pressure on abolitionists.