Well I took the British Raj and that does give a huge boost of MP. I went from 770K to 1.3 million. Oddly, ,when they surrendered, I 'lost' 150,000 MP. Maybe there is more resistance after the surrender and you get less MP? It is October of 47 and I have to say, this game might need a War Exhaustion meter. I highly doubt some of these nations would still be fighting into year 8 of a war. For example - NZ has lost 375K men. That's a massive amount! South Africa 300K. Australia has lost 900K. As some point there has to be a breaking point. Even the American's can't be too thrilled about 2.5 million losses - especially because they joined the war they weren't attacked. Would isolationist America put up with that amount of losses? As it stands now the Axis is 78% of the war to victory over the Allies but the only real way to beat them is invade America. This should not be the only way to end the war. Which Axis country even goes to war if they know in 39 the only end is invading America? It's a fun game but if I have to take China, Australia and the US too as Svea RIke it feels less like Grand Strategy and more like Risk. Some sort of War Exhaustion might be in order.
Another factor worth considering - your MP should probably go up the longer you occupy a country (and the partisans go down). England is almost a mini-game in itself with the partisans and constant UK and US invasions. None of the Axis have carriers so we can no longer prevent landings. The Allies have 3 one or two hex footholds (by Plymouth again, by Newcastle and near Scappa Flow but I have them hemmed in by Land Forts and even when they land a bunch of divisions in one of the hexes they can't break through. There was one fairly thrilling one near Plymouth where they encircled a couple of my divisions and almost broke out but I managed to push them back. Still - at some point they have to accept a peace deal it would seem. After 8 years of war I think everyone is pretty much exhausted.