As a complete novice to history (as I’m sure you can tell from the question) I was shocked to discover that Prussia still existed into the 20th century. I had always assumed that it was in some way incorporated into other countries by that point but it appears to have existed simultaneously with Germany around the period of the First World War.
So my question is more specifically, during the period of the early 20th Century, what was the difference between Prussia and Germany and how did they interact?
I realise that some of my complete misunderstanding might be related to the workings of the German Empire, so I would love some expansion on how the German Empire was governed and organised.
Thank you for any responses.
Okay, basic German federalism crash course I guess.
The "Germans" are a rather large cultural unit. The German nation consists of several smaller regional entities. Historically, some of these have been called 'tribes' (Grmn.: Stämme). Such entities might include the Bavarians, Mecklenburgers, Saxons, Swabians, Westphalians, you name it. Don't name the Austrians though, they don't like when you do that.
One such regional entity was the Prussians, Germans that settled in the geographic region of Prussia, which roughly reaches from southwestern contemporary Lithuania to centralnorthwestern contemporary Poland. This group of Germans started settling in these areas as part of the Ostsiedlung in the 1200s, and most of them were expelled in the late 1940s, effectively eliminating the Prussian regional identity as a separate unit (apart from the home expelled (Grmn.: Heimatvertriebene) interest groups in Germany, which are now rapidly dying out due to lack of interest by younger generations).
It comes from this traditional sub-separation of the Germans into regional identities that Germany takes it strong history of federalism, with the contemporary German state still proudly carrying the title of 'Federal Republic'. The states (Grmn.: Länder, often (incorrectly) referred to as Bundesländer) of contemporary Germany include allusions to the old regional identities. You have Bavaria, Baden-Württemberg (a merger of two separate identities), Saxony, Thuringia, and some more of the old homies, as well as some new creations.
What the current German state lacks is a Prussia. Prussia was not created as a federal state because the Allied occupation forces dissolved it in the 1940s because of the supposed tie between Prussia as a subnational political entity and German diplomatic militarism.
Previously, Prussia had very much been a subnational unit. Germany had a federal-style subdivision into individual units during all previous iterations (even though it was effectively declawed between 1933 and 1945 because of the Nazi Gleichschaltung, which famously hit then-social democratic Prussia with the Preußenschlag).
The chamber in the German political system representing the demands of the federal member states (the 'upper house' to use the politically established term) has been traditionally known as the 'Federal Council', Bundesrat (until 1902: Bundesrath), and such an institution still exists as the upper house of the Federal Republic of Germany today.
During the German Empire, the Federal Council consisted of initially 58 seats, later upped to 61 when Alsace-Lorraine was added in 1911. Of these seats, 17 were held by Prussia, by far the largest and most populous state in Germany. It was in fact underrepresented proportionally to its absolutely overwhelming population dominance (in terms of area, Prussia even made up two thirds of all of Germany), but its 17 seats were still far more than Bavaria's 6 in second place. Prussian votes were thus absolutely essential to get any sort of working majority.
Prussian power was further exascerbated by the fact that the Prussian Minister President, i.e. the 'Governor' (to use the American term) of Prussia, was often Reich Chancellor of Germany in personal union, and thus oversaw both the cabinet and the upper house. Prussia additionally traditionally held the chairmanship in almost all Reichsrat delegations (except for Foreign Affairs, which Bavaria negotiated for itself as a condition for its accession to Germany).
Whatever you think of Prussia as a political entity and its alleged inherent cultural militarism, it is very clear that the size and population weight of Prussia inside the German Empire (and later the Weimar Republic) hindered any serious attempt at federalism. In fact, Prussia's vote share had been even higher between 1867 and 1871, during the short-lived North German Confederation, in which it held 17 of 43 votes - five short of the 22 required for a simple majority. The compromise made by the Weimar Constitution of 1919 had been the clausula antiborussica, in which Prussian electoral power was artificially and specifically limited, despite the fact that Prussia contained approx. two thirds of the country's population.
From the pure standpoint of political science, Prussia in the form it had between 1867 and 1945 had to go to not lead to massive distortions of electoral power. Some two thirds of German territory and population were represented by delegations that initially held just under half of the political power in the upper house, which eventually went down to under a third.
Whether or not the Allied decision to abolish Prussia in 1947 was motivated by such specific goals of enabling Germany to have more democratic electoralism is doubtful, but it's an acceptable side effect nonetheless.