How was the Emancipation Proclamation constitutional?

[True Federalist (진정한 연방 주의자)]

The Emancipation Proclamation was deemed constitutional as a war measure.  It essentially confiscated as contraband of war all the human property of the area still in rebellion, and then freed it as surplus to requirement.  It didn't free any slaves in the area still loyal to the United States precisely because that would have been unconstitutional.