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The Prussian Confederation is made up of three regions. Greater Prussia-Hannover, Luxembourg, and Denmark.
Denmark and Luxembourg are autonomous regions within Prussia. They are represented by Prussia internationally. While Prussia controls immigration and external diplomacy, the regions of Luxembourg and Denmark make their own laws, and have a separate constitution from the rest of Prussia. As well they also have their own ID and Passports versions.
Militarily they are Prussian defended, however Danish and Luxembourger-only Units exist as well which are equipped and funded by Prussia. Soldiers from these units will only be deployed to Foreign conflicts and PeaceKeeping missions if they volunteer. This was part of the Annexation agreements of 1757 and 1832.