Decisions by the President, Congress and SC decreeing the inhabitants including unionists in the confederacy to be treated as foreign nationals is defacto recognition of the confederacy. This should put to rest the arguments on this forum on whether the CSA was a sovereign power or not.
They weren't decreed as if "foreign nationals" by the USA. Just do
mestic enemies in a
civil war; the laws of war being largely the same when fighting either foreign enemy countries or domestic enemies in revolt. However, to the extent under the customs of war domestic enemies in rebellion were to be treated with more severity, the Lieber Code for the US Armies from 1863 directed the same.
Relative to the Constitution etc. they remained during the war US nationals, citizens etc., found in insurrection and rebellion, and potentially subject to prosecution in the courts (once reestablished). Neither the President or Supreme Court suggested the people in the Confederacy were other than US citizens, and Congress passed acts specifically relative to them as citizens (like the Confiscation Acts of 1861 and 1862).
The Southern Confederacy during its brief existence certainly claimed to be "sovereign" over its territory, using what it called expanded and combined "State sovereignty" against the United States. Its evidence was war (Jeff Davis, Rise and Fall, II, 281). But it attempted to employ citizens of the United States for that purpose rather than foreigners who owed the US no allegiance.
During the war the Supreme Court observed in the Prize Cases their insurgent cause in waging the rebellion as a war was to absolve those States' citizens of US Jurisdiction if possible...
The war ended without so absolving them of their allegiance to the USA, and all were still subject to potential prosecution in courts of law. Most were given amnesty or pardon by the President between 1863-68, or later relieved by Congress from any disabilities under the 3rd section of the 14th Amendment for rebellion or insurrection.
While during the war the United States conceded the status of belligerents in a civil war upon the Confederate military (as an Army of US citizens acting for States in rebellion), they never admitted any sovereign
political authority in the Confederacy... de jure or de facto...
For a comparison, Chief Justice Chase in Thorington v. Smith (1868) observed the government of Cromwell over England was certainly de facto, in that upon restoration of Royal authority, many of its acts remained on the books. In exact contrast, the Southern Confederacy left behind no law etc.
of itself upon the United States. Chase observes while some might call it "de facto" government during its brief exercise of power, the Confederacy was merely a temporary "paramount force" over the Southern States...
None of the above exactly any surprise. For example from well before 1861 Thomas Jefferson in 1811 observed the mere ability of unsound States to employ their civil or military powers against the USA cannot handily sever the Union...
Or President Jackson in 1832, observing thirty years before the Prize Cases in 1862 that the States cannot absolve their citizens from allegiance to the Union in such cases either...
From the beginning of the war, etc. President Lincoln, Dec. 3, 1861 reiterated the People of the South remained US citizens, and not foreigners.
During its course... Lt. Frank Haskell, USA in 1863...
At its close, as noted by General J.L. Chamberlain, USA...
Afterward, as noted by Gen. J.B. Gordon, late CSA...
Into the the next century, as observed by Harry Pratt Judson...
And to the present century. The US courts most recently found in the case of Griffin v. Veterans Affairs, for the latter. Given the US Government's maintenance of the graves of Confederate War dead, etc. as "United States citizens" who fought in a civil war, is yet observed...
Bringing the