One of the first things the Nazis did do in the context of their Gleichschaltung policy (i.e. the total control of all facets of society along with the removal of factions outside of said control) was to remove the autonomy and agency of Germany's various states. This development actually predated the Nazis; in 1932, Hitler's predecessor as chancellor Franz von Papen, had staged what essentially was a state-led coup against the state government of Prussia (which was led by the social democrats at the time) and brought it under direct control by the imperial government and placed a centrally-appointed Reichsstatthalter or "imperial governor" at the top. The legal reasoning behind the so-called "Preußenschlag" was shaky at best, and attempts by the former government to contest it led to nothing.

The Nazis continued this idea of "centralisation", if you will, that was begun by the Papen government (which, to be fair, wasn't a fringe position at all but instead was prominent throughout large parts of German society pre-1933). On January 30th, 1933, Hitler was appointed chancellor; during early March, "imperial commissars" were appointed for those states who weren't yet governed by the NSDAP on the grounds of a supposed emergency situation threatening the nation's stability. On March 24h the "Enabling Act" was passed which gave Hitler near-absolute power and the ability to act independently of parliament, and a week later the first of two laws that de facto removed the states' autonomy was passed at well ("Vorläufiges Gesetz zur Gleichschaltung der Länder mit dem Reich"). With this law, every single state and municipal parliament was dissolved and replaced by a new parliament formed not after an election, but instead following the results the respective states and municipalities had seen in the last Reichstag election, effectively handing the power to the NSDAP almost everywhere; at the same time, the new state governments got the power to act independently of their respective parliaments, too.

On April 7th, a second law was enacted ("Zweites Gesetz zur Gleichschaltung der Länder mit dem Reich") which introduced imperial governors for the rest of the states. While the local states' governors now were all NSDAP, they in theory had had the ability to act independently of the imperial government. This was now also removed. The process was de facto finished by January 30th of the following year, when the "Gesetz über den Neuaufbau des Reichs" formally abolished the states' sovereignty as well as all state parliaments. Two weeks later, the Reichsrat as the second chamber of imperial parliament representing the states was abolished as well. The state governments continued to exist, but they were (in theory, at least) completely subject to the imperial governor's whims.

That didn't mean that there was no particularist element to German politics anymore, however. While legally speaking the imperial governors were supposed to be subordinate to the Imperial Minister of the Interior, Wilhelm Frick, some of them interpreted their role quite liberally and tried to extend their local power as much as possible. Frick quarreled endlessly with governors like Göring in Prussia (who, strictly speaking, was only its prime minister but had been given all powers of a governor by Hitler). On the other hand, some of the prime ministers like Siebert in Bavaria proved to be quite skillful in outmanoeuvering their governors and building up a power base of their own. Add to that the parallel party structure of the NSDAP, whose "Gauleiter" not only wielded a lot of de facto power, but throughout the years also gained a bunch of official administrative powers, and you can see why Wilhelm Frick would have loved nothing more than to formally conclude the abolition of the states and replace the chaos and the constant power struggles between governors, state governments and local party leaders with a more streamlined top-down hierarchy culminating in Berlin. The imperial government never quite got around to it, however, and after 1939 all further plans were shelved to be reactivated after the war.