Virginia 1832: John Floyd includes a plan for gradual emancipation of slaves in his annual address to the General Assembly of Virginia as part of his "Virginia Plan" for economic growth. He is barely successful due to the ravages of a large Nat Turner slave rebellion (the POD).
I've just avoided or significantly changed: Texas' Revolutinary War, The Mexican-American War, and the Civil War.
Likely progression of events, IMO:
Texas annexed, along with a border from the Rio Grande to the 30th parallel; Baja CA to the US.
Oregon border secured to the 49th parallel.
By 1858-1860, National Floyd Plan enacted. Slave owners compensated, appeased by promise of lower tarrifs for period of 20 years.
1861-2: US intervenes to stop French/British intervention in Mexico. War for North America? US takes Canada, with help of Fenian rebels?
The more interesting Peace: the US is HUGE.