On German colonies (and colonies in general): Decolonization is not predestined imo. There's large amounts of resources in those place and the people can be put to productive use, either for factories or as soldiers, both which ws barely starting by 1914. They're also useful as extra ports.
Yet they also tend to be money sinks as well, granting the owner less than what was returned. They do have a use as ports, but only one of those (Togo) would be relatively closer to the Americas than any other base.
Any return on investment would be decades down the line, far past tthe point where an invasion attempt would be made.
On A-H navy: The short-leggedness of the A-H navy was the result of the mission and the subsequent construction. A new mission and new plans for ships would result in a longer ranged navy as old ships are replaced by new ones. With the French/Italian defeat and arms limitations treaties and the Ottoman backwardness A-H would be the only one left in the Mediterranean. While A-H never really showed interest in colonies things like Malta or Greek islands are always a possibility as well as basing rights in Turkey and the newly "independent" North African states, plus there's German Suez. There's imo plenty incentive to go further out of the Adriatic, and after the war A-H would also be militarily more "reawakened" after spending the past 50 years treating the military as a dumpster for nobles.
Yes, arms limitations treaties, but those are not destined to hold on permanently. And you still have to be economical about these vessels - they're designed for 20-25 year cycles. Plus, why would AH want to expand out of its littoral region when it could become content reigning supreme on the Med? If AH can try and make parts of the rim its sphere, why would it need to go further afield, aside from perhaps a vanity colony?
Also, how do the Germans get Suez? That gets back to the age-old question of how the Germans are able to force the British to hand back over the colonies in WW1.
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France & Russia are both in bad places. They both could go downhill into a death spiral, though that's leaning on the scale to assume they'll both fall just into place - Russia especially.
As for the scale of Mitteleuropa even at its largest and most favorable conditions, how do they manage to project power across the Atlantic, and more importantly, why? You'd have to completely rebuild the fleet to sortie across to North America, while the US would not be limited by such a problem (and after the
Sodaks and
Lex were done, the plan was to continue with more
Sodak, likely with minor improvements).
So, by the mid 20s, you're likely facing a big gun fleet of 6 12" dreads (not counting the
South Carolina class as they are too slow for fleet maneuvers), 9 14" Standards, 4 16" Standards, 6 Sodak 6 Lex along with those hundreds of destroyers and various older vessels. By the end of the 20s, you'd likely had ~12 Sodak to that number, with the older 12" ships going to the reserve. The US already had various carrier plans and would likely have a few in service by this time (and if the larger ones are chosen, they'd be more massive than
Lexington was and would be purpose built, and better optimized). By the late 20s any old armored cruisers would also have been phased out, replaced by light cruisers unconstrained by the WNT.
You're limited by the Kiel Canal, which is far more restrictive than the Panama. Yes you could expand the Kiel, but on the other hand, there were plans to expand the Panama as well.
How do you invade past a fleet that when it started was only really inferior to yourself and the UK, and after many years of buildup is certainly a peer opponent, who is also thousands of miles away and fighting on their front door? The Germans would have had 21 (really 17, should I use the same rules as I did for
South Carolina) ships before the L20, and 6 (assuming Jutland still occurs and they lose one ship during the war)remaining battlecruisers +7 of the
Mackenson/Ersatz Yorck classes. Of those, only the
Konig, Kaiser, &
Mackenson could be called long range of the battlecruisers; the
Ersatz Yorck would have reverted to the ~5500 nm range that was on the
Derrflinger. I don't know what the range for L20 would be, so I can assume it'd be modified for 8k nm like the
Mackenson, as the design was not finalized until 1918 unlike
Ersatz Yorck. The four oldest battlecruisers have a range that is not suitable for use.
AH only had 4 dreadnoughts, which both were incredibly short-ranged and not comparable with newer super dreads. The
Ersatz Monarch vessels would likely be redesigned as they were never laid down, and the original design would have effectively been equivalent to a short-ranged
Nevada class.