What is the Holy Roman Empire? I have a little background knowledge and I read a little bit on Wikipedia, but I'm still not exactly sure what it is. I know that the states under the "Empire" were still more or less independent. I also know from Wikipedia that the Holy Roman Emperor was the protector of the Catholic Church, and that the Holy Roman Empires consisted of mainly Germanic states, but that's about all I know. Also, who could be named Holy Roman Emperor? Was it Germanic Kings only?
Imagine the USA electoral process: you don't technically elect the president, you elect someone into the electoral college of your state who elects for the president every 4 years, and you elect some members of congress and the senate every 2.
Now imagine that congress doesn't exist, every state gets 1 appointed senator, and you, the filthy lowborn peasant, obviously don't vote for another filthy lowborn peasant to choose the heaven-appointed man who will lead the German Reich. Also, irrelevant states like Wyoming and Rhode Island aren't worthy enough to choose the next president. In fact, only economically/militarily powerful states like California, New York and Washington D.C. (just imagine it is a city state and not the capital) can. The smaller states can only participate in the Senate, or Diet, where every state sends 1 delegate. The Diet itself is an institution whose power waxes and wanes depending on what period of time you are looking at. For example, they did formalise who would be the electors of the HRE in the Golden Bull of 1356, declared by the Diet of Nuremberg which every state votes in.
The criteria for the man who becomes emperor has an added requirement: he must be able to claim lineage to Charlemagne. However, nobility in the olden days interbreed often, by about 400 years later just about any duke or lesser noble can become a potential candidate. Notice that this process is NOT hereditary, but by the 15th century the Hapsburgs became so powerful that they control the Imperial office and were re-elected every time.
The new emperor then becomes de jure liege to all the states. But like the president in the early days of the USA, his word is not law. Instead, it is up to the state to implement the changes. This leads to the major problem of the most powerful states in the Empire competing for power, much like how if the governor of New York told the governor of California to stop trying to make rap music because the east coast is obviously better, California would not listen. As a result, the HRE often falls into civil war, the biggest being the 30 Year's War from 1618-1648, which resulted in the Emperor being given even less powers.
In essence, the HRE is kind of an elected monarchy with an appointed senate, but then again not so much.
When elected, the Holy Roman Empire would not gain complete control over these areas, instead these areas all had their own rule or administration which was generally inherited.