Good example. The person who actually ended slavery in the US, Abraham Lincoln, didn't support abolition until the military advantages of emancipation became obvious enough that he could sell it to the people. For a long time he supported some slavery improvements, but specifically did not support abolition - which very much helped his political career and put him in position to emancipate.
We might also note that what Lincoln did -- the Emancipation Proclamation -- abolished slavery only in areas that were not subject to the Union, making it questionable as an act of governance. Slaves in Union territory were emancipated by the 13th amendment three years later.
