If a player offers to be vassalized, is there a mechanic that allows him to change that status without initiating a war?
Yes, you can end it without war.
What the hell happened to South American Spain and GB, and didn't Sweden just spend the entire game sat in Japan? What was going on there? Or to paraphrase the question, is there a game to be had outside Europe?
The glory in EU3 multiplayer is in Europe. There are some campaigns that could get interesting in other areas, but in this one it was very quiet outside of Europe, except race for China/India.
I was pretty surprised that Prussia went for Scandinavia rather than trying to get the much nicer provinces in Germany, though I suppose that reflects Brandenburg's much poorer starting position. The Prussian military reforms didn't seem to be game changing either.
Brandenburg starts in a terrible position. It has second worst starting sliders in Europe (only Milan has worse), starts in a PU and most neighbours either wants it dead or relatively weak. One diplomatic blunder can get it crippled or annexed.
So the usual plan is to get out of PU in the first year, complete mission on Pommerania, vassal minors that join in the war and wait for 50 legitimacy to start forcing personal unions. This usually takes 5-10 years before BB can start rolling in Germany. Which means that in that time a good Austrian player can claim most of HRE around Brandenburg (or simply annex it).
Here is my previous Brandenburg game in which Austria and Poland were not nearly as skilled as Rayzee. Austrian player was not fast enough with HRE minors which gave me opportunity to take it for myself. So as Brandenburg, you can go crazy in Germany only if other players allow you or they are not that good. This map was from 1492.
Rayzee is a tough player so I had two options, seek help from France or Ottomans before game start or make a deal with him. There was no interest from those two, so I made a deal in which he got good chunks of HRE. Of course, Rayzee claimed our agreed border in those opening years as expected. That 200 year German alliance in which we bled together against France was a result of it, because I have been extremly weak for most of the game.
The only easy expansion in this game was Scandinavia. That is where I actually got my power. Even though I had the poorest land in Europe, it was still good enough for conscription centers.
Prussian military reforms were definately game changing because combined with CC's from Scandinavia, Prussia had finally become a great power. It was stronger then Austria for the first time in the game, so the German alliance ended and with it the game.
You where the one who ended the game by creating the alliance of doom and told us that it would never end.
Neverending alliances are never any good, especially when one nation (France) sayed that they would just fight wars to give his friends land and not demand anything on his own.
Eh, "never ending alliance". I think I told everyone that I've talked about it, that I'd take 1v1 with Austria. But there was almost no chance of it because of the alliance with Italy and Russia.
So I fought Austria/Italy last session. I also didn't wait for France, even though I knew France was joining soon because that would mean Russia would dow me and it would become silly. So I peaced Austria/Italy. Russia then dowed me anyway to retaliate against France?
Then Austria and Italy became Russian vassals and Russia invaded Ottomans. So I basically wasn't able to expand anymore unless I invaded Russia. I could wait for them to murder Ottomans then come for me again. Or I could build some troops (invaded with only 600k and 150k manpower reserves) and drive through Russia and try to help Ottomans in Caucasus where it looked like we could win.
In short, me and France never fought together in the last session. So much of this "alliance of doom".