We'll skip the HRE and the French Puppet Confederation of the Rhine and just stick to the 19th century.

With the dissolution of the HRE in 1806 and the final defeat of Napoleon in 1815, the various German states were independent.

They chose to form the German Confederation which was primarily a defensive pact but also established a constitution and assembly for which delegates could vote for binding resolutions, however they needed to be unanimous. Also this wasn't "one state one vote" votes were divided by power & population. States like Austria, Prussia and Bavaria having the top votes, and smaller weaker states being grouped together for their vote. The Diet had two separate voting styles. When voting for general affairs, there was a total of 17 votes distributed across the states. And if laws or new institutions were being established, a diet of a total 69 votes were distributed among the states.

The Confederation was seated at Frankfurt with the Emperor of Austria as the President of the Confederation. This is "presides over a meeting" meaning of president, not the American style of Head of Government Executive Officer President.

The Confederation established a Federal Army made up of primary Prussian and Austrian troops who were garrisoned along the border of France in federal forts. These were separate from a state's own military fortification.

The Confederation proved its worth as an organization during the "1840 Rhine Crisis." we won't get to deep into that event except to say that event was when the French Prime minister attempted to reannex the Rhineland by bringing up a defunct Napoleonic treaty.

The Confederation rallied troops to the frontier and committed to building more fortresses and defending German territory. This event inspired many national artworks such as the song and paintings "The Watch on the Rhine."

But it wasn't all sunshine & roses in Germany. An intense power struggle existed from day 1 between Austria and Prussia for who would be the leader of Germany.

There was even a short lived German Empire established during the 1848 revolutions where delegates voted to transform the confederation into the empire and offer the crown to the King of Prussia. Same as above, we won't get into the weeds of that event either except to say that the King ignored the offer and the movement for that incarnation of German Empire died on the vine.

But what that showed was that the divisions within the Confederation were growing AND that the confederation wasn't satisfying the German peoples anymore, they wanted more.

The Prussian-Austrian rivalry came to a head in 1866 when Austria lead the rest of the Confederation to war against Prussia. This is known as a Bundesexekution or federal execution where the Confederation can war against a member who is violating its laws.

However, Prussia would defeat Austria and the Confederation in 6 weeks with one of the stipulations for peace was the dissolution of the German Confederation.

Prussia would establish the "North German Confederation" with many of the defeated Austrian northern allies. This was a far more common centralized state with Prussian control, however the North German Confederation and its direct successor, the German Empire (they used the same constitution) was still a federal State and as such still had member states with local autonomy.

The Southern German states were allowed to form their own confederation in the treaty but never did. They operated as fully independent states for a grand total of 4 years until they joined Prussia against Napoleon III's French Empire and chose to join the established German Empire, officially proclaimed on January 1st 1871.

Austria, with its own Habsburg patchwork Empire, would stay forced out of the majority of German affairs; a German State and German Empire outside of Germany.

Here's a english translation of the German Confederation constitution

https://en.m.wikisource.org/wiki/Final_Act_of_the_Congress_of_Vienna/Act_IX