all forces in america retreat to the coastal areas
soon after the army is at the coast, all thats left is a thin line of defense to hold against the onslaught of SSA and ASA's forces
even later, masses of large trade/supply convoys that were harbored within the most northern areas of america flee back to germany using the route protected by the KSSR, under the protection of what is even actually left of the american-prussian navy after the strikes.
(ignore the estimated number of dead, and there's obviously more than one explosion)
nuclear devices go off within prussian-controlled territory of america, ultimately destroying and pulverizing major cities, and utterly irradiating a large radius of the east coast once again.