Of course, Baltic Republic never existed. Its my own term for a Baltic state that I've created in some Paradox games and that has some resemblance with real life ideas. But none of the Baltic Confederation or Baltic Federation or Baltic Union ideas ever went farther than couple of discussions. United Baltic Duchy - thats a state that did indeed existed, at least on paper.
With Germany winning the WW1 OR Entante allowing Germans to do what they please in their eastern held territories in 1918-1920, a German puppet-states like United Baltic Duchy might very well have survived. Because even after defeat in western front Germany was clearly the leading power in the region between Baltic and Black seas. In fact, such interesting people like von der Goltz (liked by Finnish, hated by Baltics
) dreamed that he'll organize a Baltic puppet under leadership of Prussian power, rebuild German armies and establish a German-loyal Russian government. And with a Russia backing Germany, soon re-start military activities in the west. But, Entante by direct and inderect military support helped to ensure that Germans more or less (..) but do respected their defeat and retreated from this region.
Portugal-Brazil
Yes, Brazil left, but it was an interesting concept. Even more so because that state would have colonies in Africa.
"Baltic republic
OK, so let me get this straight.
You're gunning for a Baltic Republic consisting of the three Baltic states,
plus Eastern Prussia?
So why did they not do this in real life?"
Yes, pretty much. I'm advising that a way to make this region more interesting and not just a pushover between German-power and Russo-power is a buffing and consolidation.
They did not do this in real life because: 1) Surrounding powers like Sweden and Russia centralized in 15-16th centuries much better than local Livonian confederation ever managed. And whenever state centralized it tries to limit consolidation of power in its near surrounding. Thus, growth of powers on eastern shores of Baltic sea were impossible. 2) If Lithuania stays independent (meaning - doesn't form Polish-Lithuanian commonwealth) and manages to sustain itself longer against Russia (not an impossible task), then Eastern Prussia and modern Latvia and Estonia might very well in time come under its control. Well, it might even happen with Polish-Lithuanian commonwealth, so it might be both ways. So there was some possibility there. 3) In our timeline, post-ww1 no Baltic confederation happened because: a) couple of countries had border conflicts, namely Lithuania and Poland that totally destroyed any serious regional cooperation; b) when in 1930s Lithuania and Poland had let their mutual conflict decrease to almost reasonable levels and some chance of serious regional cooperation arouse, the historical great powers (namely Germany and Soviet Union) of the region had regained their influence and neither of them planned to allow any kind of serious regional cooperation between countries Finland to Romania.
But, if: 1) no Lithuanian-Polish war; 2) abit more reasonable Polish foreign policy; 3) idea of regional federation abit more popular, 4) Germany and Soviet Union abit less successful in their foreign policy, then -> some kind of Baltic or "
Intermarium" cooperation is a quite realistic chance.