games

I'm by no means a Vicky 3 expert, but most times I've found my economy exploding like that was usually due to the same few common issues:

1. My construction sector can't afford the switch to new materials,
2. I changed the production for certain sectors all at the same time (e.g. switching to nitrate for farms, dynamite for mining all at once)
3. A loyal interest group just became disloyal, and I lost their bonus.
4. I was cut off from a trade group/sphere/whatever they're called that I was relying on.

The way I've found to help combat this is by only ever tweaking the individual buildings one at a time at the state level, and never switching all at once. I also make ample use of subsidies to prop up basic industry such as forestry so that I can handle my own basic necessities. Finally, don't be afraid of switching back to more basic modes in your buildings if they can't get what they need. The important mid-game goal is to have a completely self-sufficient steelmaking process and to start churning out both engines and steel-frame buildings. As for diplomacy and warfare... I have no clue. I only ever play Vicky 3 like it's a city builder lol.

Fair warning: I have no real clue how to progress or play optimally. The best I can manage with my limited knowledge of the game is to have my peasants well-fed and happy while still having a positive economy