After the Second Peace of Paris and the work of the Vienna Congres, a new map of Germany was drawn. The Polish-Sakson question was settled. Prussia only kept the Posen area of Poland while the rest was added to Russia as an autonomous Kingdom in personal Union with Russia. This was called Congress Poland, after the Vienna Congress that had created it. Prussia took large parts of Saksony, but the remnant of the Kingdom was allowed to survive, contrary to the first, Russian, scenario in which Posen would not have been returned and Prussia would have swallowed Saksony whole. Prussia also gained a lot of territory in the Catholic Rhineland and Westphalia, previously owned by Wittelsbach and ecclesiastical rulers, where Prussia had possessed some assorted small counties before.
As a result Prussia was firmly shoved towards the west, back into Germany, strengthening the German character of the state.
The reappearance of the red border does not signify the return of the Holy Roman Empire. Instead a loose German Confederation was put in its place.
The Prince of Orange-Nassau, who had lost his German domains, had returned to the Netherlands where he became first a sovereign Prince and then King, instead of Stadtholder as his father had been. The new Kingdom was enlarged with the former Austrian Netherlands, or Belgium, as a buffer state against France. The King however wasn't restored to his German lands. Instead he was made Grandduke of Luxembourg. The Grandduchy was however a province of the Kingdom of the United Netherlands, while at the same time a Grandduchy of the German Confederation. In a dynastic sense it took the place of the Principality of Orange-Nassau within the dynastic treaties and settlements of the House of Nassau.