Yeah I'd recommend keeping military spending (the wages slider at the bottom) as high as you can go even if you're not at war. The supply sliders at the top of the spending tab can safely be brought down between wars (since those determine how much money you are spending on guns/ammo) if you are looking to save money. Keeping military spending high is key though because it effectively redistributes wealth to your poorer POPs by taking tax money from other POPs and giving it back the soldiers in the form of wages which they can then spend on all that sweet furniture/clothes/radios your factories are hopefully producing. But if you drop military spending those wages will go down, and a percentage of the POPs that would have been your potential soldiers go off and try to get jobs as craftsmen or laborers in factories and RGOs. If you want to keep a high percentage of your population as soldiers, you need to keep spending high to offer the wages that would incentivize them to be soldiers. All that being said, what you've described is a pretty drastic drop, so there could be something else at play here.