Answer:
That statement is true.
Step-by-step explanation:
One example of this would be The New York Historical Society presented an exhibition on slavery in that state.
Most citizens of United States probably remembered the Northern States as the ones that marched toward the Southern Statas in order to free the slaves under the leaderships of Abraham Lincoln. Even though this is true, Most people tend to forget that Northern States also used Slave labors for the plantations before the industrial revolution.
The only reason why northern states supported to end slavery was because of industrial revolution who provided machines that can replace the slave labors. Without those machines, Northern States probably still used the slaves along with Southern States and the Civil war never occurred.