Article II Section 2.
The President shall be commander in chief of the army and navy of the United States, and of the militia of the several States, when called into the actual service of the United States;
Article I Section 8
To provide for calling forth the militia to execute the laws of the Union, suppress insurrections and repel invasions;
To provide for organizing, arming, and disciplining of the militia, and for governing such part of them as may be employed in the service of the United States,
To provide for organizing, arming, and disciplining of the militia, and for governing such part of them as may be employed in the service of the United States,
If you accept the flawed claim that secession is "insurrection", then you can make an argument for using the military to put down the "insurrection".
But how do you go from putting down an insurrection to a blanket seizure of "property" for the entire region? Especially in light of Article 4, section 2?
What about "due process"? Or is everyone within some geographical region automatically guilty and convicted of crimes against the state?
Suppose the order was to seize all farms, or all horses, or all gold or silver? What is the difference between that and what was done?