Drang nach Osten, "Push to the East, a Germanic Expansionist philosophy gaining traction years before Hitler was just a twinkle in Alois’ eye.
And the (Germanic) Austro-Hungarians had shown their proto-Nazi tendencies with ethnic cleansing of Slavs in WWI
As far as I know, though, some of the Baltic Germans began cooperating with Germany even before the Bolshevik Revolution occurred in Russia.
You might very well be correct here. Of course, I believe that I previously mentioned that the free or cheap land and/or the economic opportunities in the Baltic states might encourage some/many ethnic Germans to settle there.
Well, Yes; after all, a lot of what I am writing here is speculation on my own part.
Didn’t many French people settle in Algeria, though? Likewise, didn’t many British people settle in colonies such as Canada, Australia, New Zealand, and South Africa?
Indeed, colonization appears to have been something which was successful for some of the European colonies in the 9th and early 20th centuries but not for other European colonies.
I am unsure that the Germans would have been bucking a trend, though. After all, many British people do appear to have immigrated to colonies such as Canada, Australia, New Zealand, and maybe South Africa in the 19th and early 20th centuries.
The thing is, though, that even without such an explicit policy, some/many ethnic Germans could nevertheless settle in Eastern Europe, such as in the Baltic states. Indeed, this might be especially true for Eastern European (including Baltic) cities and suburbs; after all, Germany was certainly a rapidly industrializing and urbanizing country in the late 19th and early 20th centuries. 
Large-scale population movements don’t necessarily need to be planned, though. After all, did the U.S. plan its own historical westward migration, or did it simply happen on its own due to socio-economic factors and reasons?
They wouldn’t–unless perhaps they would have been German nationalists with a love of the German farmer. Indeed, perhaps a certain Austrian-born German nationalist with a Charlie Chaplin mustache might fit this description. 
Surrounded? After all, some cities in the Baltic states, such as Riga, already had a large ethnic German population even before the start of World War I! Heck, ethnic Germans made up a whopping 43% of Riga’s total population in 1867!
Plus, as I have previously mentioned, the opportunity to acquire free or cheap land as well as the economic opportunities in Eastern Europe might have encouraged some/many Germans to settle there.
Yep–Drang Nach Osten, or, in English, Yearning for the East.
Also, fun fact–the concept of Drang Nach Osten appears to be an attempt to build up on the Medieval German Ostsiedlung.
In addition to this, here is a crucial question–exactly which factors caused Americans to move from the East to the West in the 19th and 20th centuries? The free or cheap land? A belief that the West had a nicer climate than the East? Some other factor(s)? A combination of factors (and if so, exactly which ones)?
Any thoughts on this?
I would say yes, as a public-private partnership between the Federal government and the railroads.
The Homestead Act was an explicit pro-migration policy: farm a certain size chunk of land for a certain number of years (5, IIRC) and build a house on it, in the undeveloped Western territories, and the land is yours.
The government also granted the railroads strips of land across the territories that were significantly wider than needed for the railroad infrastructure itself. The railroads then sold the excess land to settlers cheaply to develop mid-route traffic and promoted settlement by advertising both in the East and abroad. Notably, the government granted the railroads the excess land in a checkerboard pattern, keeping every other chunk (a surveying township, IIRC) for itself.
Anyone play the Kaiserreich mod for Hearts of Iron 2: Darkest Hour? It’s an alternative WW2 game in the aftermath of a German victory in the first world war. Austro-Hungary and the Ottoman Empire survive, France and Britain get taken over by radical leftist regimes. Lots of fun.
Anyway, in this history, the Kaiser never abdicates, Estonia and Latvia become a German duchy with an active resettlement policy, Lithuania and White Russia have Hohenzollern rulers, and Ukraine is essentially a German puppet, so German migration is possible all the way up to the Russian border.
What about before the Homestead Act and before the railroad age, though?
Out of curiosity–where exactly is the origin of the ethnic German migrants to the Baltic states in this game? Also, exactly how many ethnic Germans settle in the Baltic states after the end of World War I in your game?
The origin is from Germany. The alt history in the game posits a Germany that becomes a world superpower, but less powerful than the USA of our world, and surrounded by rivals. It’s a very conservative Germany, socially and economically, which spurs out-migration to the east and Germany’s African and east Asian colonies for those seeking opportunity.
As for numbers, it’s abstracted, though there’s an event for the Baltic duchy to represent German population growth reaching a tipping point. But Russia still has influence in the area (you can bring the Tsar back in this game, or go more left wing). The overriding theme of the game is that moderate, democratic governance has been largely discredited in the wake of the war, in favor of extreme left and right wing movements.
Just from Germany? Not from Austria-Hungary and/or Russia as well?
OK.
OK. Also, though, can you (as Germany) annex the Baltic duchy/duchies after they have reached a tipping point in regards to their German population?
Even before the present Constitution, Congress adopted the Northwest Ordinance and Land Ordinance which provided for surveying and selling undeveloped land in the territories and created a system of government for the territories that scaled to population (governor without a legislature with less than 5,000 citizens, then a legislature, then a new State when 60,000 citizens was reached). Wikipedia on the Northwest Ordinance and Land Ordinance of 1785. Not quite the active promotion of development as with the later Homestead Act and railroad land-grants – merely surveying land doesn’t guarantee anyone will buy the lots – but definitely a plan or framework for development instead of allowing it to happen willy-nilly.
Thank you very much for sharing this information with us!
Note the abroad part there. Much of the advertising was all over Europe, from Ireland to Russia, Norway to Italy. Cheap land, just buy a steamship ticket (the steamship companies also advertised) and a railway ticket, and it’s yours. Then when they get there they find that the same railway has a monopoly on shipping to the area and it’s not cheap to send their grain or other produce to market.