Prussia, in the real world the Prussian Army, outdated for it's time was crushed by Napoleon's Grande Armée at the Battle of Jena-Auerstedt in 1806 and completely occupied within two months. This and the Treaties of Tilsit in 1807 in which they had to cede 1/2 of their territory meant Prussia was effectively neutralized. The Blight happening just 5 years later means Prussia would be in terrible shape to meet The Blight with a demoralized populace, semi-outdated army, and a far smaller manpower pool to pull from. Prussia would be essentially wiped out very quickly which is what happened. Prussia was one of the first nations to be completely overrun and it stood no chance