The autonomous Kingdom of Prussia found an end when the German Empire was founded in 1871. While the policies of the Empire and those of the Kingdom of Prussia that was now a part of the German Empire were closely related and aligned, not at least by the fact that the kings of Prussia were also the German emperors, it still doesn't change the fact that the kingdom of Prussia stopped existing as a wholly autonomous political entity to become a part of the Empire – which was something they wanted and championed for.

With the political revolution in Germany in 1918, Prussia was transformed from a kingdom that was part of an empire to a federal state of a democratic republic. The Free State of Prussia, as it existed from 1920 forward, was in itself a democratic free state that was part of the Weimar Republic, in its status and autonomy comparable to something like the Commonwealth of Massachusetts in the US. During the time of Weimar, it was consistently ruled by the coalition of parties that were the staunchest supporters of the republic, the SPD, DDP, and the Zentrum (this was even called the "Prussia colaition").

It was also what lead to the end of Prussia as a political entity with any sort of political autonomy, even within the Reich (the Weimar Republic was also called Reich as the signifier that it was federal, meaning it consisted of various states with a certain political autonomy, again akin to the United States). What happened was that in 1920 when the so-called Kapp Putsch threatened the new republican state, the SPD lead government of Prussia called for a general strike to defeat the coup; and successfully so. This helped established Prussia and its government as a bastion of pro-republican sentiment, something later governments of Weimar were very aware of.

This is why in 1932, Franz von Papen, then chancellor of Germany with a government that was only able to function because Reich president Hindenburg supported it with emergency decrees, was able to initiate what is commonly called the "Preußenschlag" in historiography. Because von Papen wanted to prepare a dictatorial government, possibly under Hitler, possibly under himself, he obtained from Hindenburg an emergency decree that would end Prussia's state as a federal state within the Weimar Republic. The state of Prussia was curtailed under von Papen himself as a special Reich commissioner and the Reich took over governing Prussia directly. It ceased to exist as a political entity to become a purely administrative one – a path furthered along later by the Nazis who instituted the same with all federal states in Germany.

The so-called Gleichschaltung lead to the end of all federal states in Germany as political entities to become mere administrative ones with the political rule being administered directly from Berlin by the Nazi government. Prussia was the first one to be hit in 1932 by Papen but the fact is de facto, it ceased to exist in 1932, thanks to the dictatorial aspirations of the ruling class in Germany. It was then that Prussia ceased to exist as a political entity as well as a legal entity in international law.

By 1945, when it became clear that the political future of Germany would start with its federal states (who in the end founded the FRG in 1949), the Allies issued Control Council Law No. 46, they stated there that

The Prussian State which from early days has been a bearer of militarism and reaction in Germany has de facto ceased to exist.

and hence they abolished it as an administrative and political entity. Now, whether German militarism was related to Prussia in case of the Second World War is a debatable opinion, though it certainly was related to Prussia's importance in the German Empire before 1918 but where they were right in that Prussia had de facto ceased to exist in 1932. Furthermore, re-establishing Prussia in its state of before 1932 was politically unfeasible: The Prussian state spanned several occupations zones and also territory that belonged not to Germany, from the Rhineland to Königsberg, Prussia had gobbled up a lot of territory over time and re-establishing all of it was not feasible due to the political realities of the occupation. Furthermore, the re-creation of the state would have been additionally complicated by the former German territory now awarded to Poland and fears of revanchist political aspirations against the new Polish state were also a factor in this.

So, there were good reasons not to re-establish the state that had ceased to exist in 1932.