if I switch to monarchy I can't afford to keep up the army.
I used to have problems like that. Have to keep growing. Cities must get to size 12 as soon as possible. And then taking more cities. I often go long on despo too due to being locked in war. But as soon as I've cleared out that first AI neighbor I make the switch. Then usually right back to war with someone else. In the middle game, I buy and trade tech more than I research it because I need the gold for upkeep and luxury slider.