Trying a United Med Italy run, starts fine, my fleet of 100mm belt CLs (because no BBs and I'm not building CAs with 20% funnel efficiency) bumrushes the Balearics and I eat it up in a snappy invasion. Their entire fleet's in the Carribean fighting the yanks, start a Naval invasion of Southern Spain, green numbers in the invasion circle.
After building more ships and exceeding the invasion tonnage requirements by three times, Spain starts to fall apart, my armies are dealing 10 to 1 casualties, Spain's asking for peace, life is good.
With Spain begging for peace, I save a backup and accept. War continues. Another failed naval invasion later, Spain dissolves one turn from the invasion completing (and likely failing again)
If nothing else, at least give provinces being actively invaded when a country dissolves to the aggressor invading it. Hell, a country dissolving shouldn't mean the end of the war, it should mean massive territorial advances for the aggressor and unconditional surrender for the country.
A government toppling shouldn't force a peace with no reparations. And Peace deals should reflect the situation the losing nation is in. Totally blockaded, naval budget hundreds of thousands in the red, actively being navally invaded, GDP in the pits, the government shouldn't be able to ask for peace and then get off with only losing some colonial territory across the world that would compromise your transports safety in a future war. Pace deals should be offered in a finalised form, and you should be able to demand terms. And if you demand something they're not willing to give you, then you should have the option of dragging the war on. I don't want Carribean provinces for a United Med run, the UK will annihilate my transports and tank my economy when I want to take Gibraltar and the UK's Med Holdings. Spain shouldn't be able to secure a peace deal and decide the terms when they lost.
Also, the US decided to break our alliance while we were both at war against Spain. Seems like a poor time to break an alliance, and I think breaking alliances should have some form of penalty across the board, like an 'untrustworthy' modifier for relations across the board.
As for invasions, it'd be cool to see invasions given some more depth. A landing phase, where every ship and gun in the invasion force gives a bonus to the invasion. A beachhead phase, where your big ships continue bombardment and your small ships reinforce and supply the invasion, and an inland phase where all you can do is protect transports, maybe give a bonus for torpedo boats acting as river gunboats? While you have enough big ships supporting a beachhead, they shouldn't be able to be pushed back. A peace deal with a beachhead or inland invasion should greatly favor ceding that territory to satisfy the invader.