"And how did the North supposedly own this property that was part of another sovereign State?"
"Own" might not be the correct word, but Federal money was used to purchase (from Spain and France) the land which comprised many of the Confederate States that were not part of the original 13 colonies. Federal resources (blood and treasure) were used before the Civil War to defeat lingering Mexican claims to Texas. Federal resources were also used to purchase land in the South from Indian tribes and to "relocate" them.
So anyone in the South should have remained in involuntary servitude to the Union? Note that "Federal" resources included resources and the lives of many Southerners. Are you denying that Federal acts were completed for the benefit of the member states at the time?
The Federal system was never meant as a means of locking in and enslaving states to a central government.