Didn't this situation used to be cothered by Johans "Shady Cabal of Financiers"? Looks like in AHD the Shady Cabal has been removed. Interesting...
(I've not played AHD yet, I have no suitable Windows machine to hand, if only Paradox made games to run on Linux. Sigh)
Well, it was covered by the shadowy cabal in regular Vic2. I don't think it has been removed, but even in the original, they only loaned a small sum of cash. (Like a couple of thousand).
What I am seeing is that the banks do not always keep up with economic growth in AHD because POPs have a harder time saving money until late in the game. By the end of the game, the national bank might have 45 million in it if I follow sensible tax policies, but prior to 1900, the banks of GPs might only have $400,000 or so in each country. If France borrows $200,000 from each major national bank, then even if they pay it back eventually, you still have a credit crunch; if they default, then what little capital the banks have is wiped out completely.
In other words, my government might be able to raise taxes to generate $100,000 a day, but various national banks might only be able to loan me a
total of 200,000. If I buy a bunch of ironclads at the same time, and don't raise taxes assuming that I will just borrow enough to cover the cost and pay it back as they build, then I end up going bankrupt because the ironclads cost more than the value of the combined national banks.
This isn't necessarily a bad thing. Credit crunches should exist and be an important limiting factor. But perhaps a "Credit crunch" warning might help. I know that my government can pay the interest and cover the debts I am incurring. There's just no warning from my finance minister saying "Hey Tsar-dude, the banks are running out of money to loan to us because France killed the national banks of Europe, even though we could pay the interest on millions more. We better raise taxes or cut the budget before we default."
I suppose the shadowy cabal could inject even more money, but that might defeat the purpose of having the national banks in the first place.