And how do you know this? And how was all the other property also not being used to make war on the United States?
If seizure is the normal response, then the normal response should have been to seize it all.
By their own words and desires, The Confederates were no longer citizens of the United States.
What they say on the matter is of no import, because the Lincoln position was that they were and always remained so. If they were no longer citizens of the US, then it can't be an "insurrection", can it?
If they were and remained citizens of the US, as Lincoln claimed in order to justify his invasion, then they remained under the rights and protection of the US constitution.
You cannot unilaterally proclaim them all "guilty" simply for being in the territory of an "insurrected" state. Each one must be adjudicated, and each one must receive "due process."
You can then legally take the property of the guilty, and spare the property of the innocent.
Proclaiming all in a region "guilty" without trial, is the act of a dictator. It is also in no manner constitutional.
“And how do you know this? And how was all the other property also not being used to make war on the United States?”
Slaves grew the food that fed the Confederate Armies.
Slaves built the forts and trenches of the Confederate Army.
Slaves worked in the mills, factories, arsenals, that made the weapons, ammunition, shells, and gun powder for the Confederate Army.
Slaves cooked for the Confederate Armies.
Slaves shod the horses and mules used to Confederate Army cavalry, artillery, and mounted infantry officers.
Slaves nursed the wounded of the Confederate Army.
Slaves offloaded the blockade runners bring in arms, ammunition and other tools of war.
slaves repaired the damaged railroads and bridges supporting the movement and supply of he Confederate Army.
Without those slaves, the War would have ended in a few months.
In addition to slaves, any property useful to the Confederate cause was usually seized, destroyed or otherwise rendered unusable by the Confederate cause.