unless you mint. your military costs have to come out of your census taxes(january 1) If you look at the expenses in the research area they are mostly paid out of trade income. If you mint(put treasury slider to right) to make up the difference you will get inflation unless you hire a Master of Mint Advisor. Hire at least a 4 star one if possible.
Even with rich nations you will go broke unless you mint. That is why National Bank and MoM advisors are so useful.They allow you mint and not get inflation.
Inflation is BAD! It makes the cost of everything go up.(regiments,ships,buildings,Stability levels,Tech Levels)
Also you can reduce military maitenance if not ar war.