Modifiers

Step 1: Ignore the alerts unless it’s a trade or a alliance

For me it would be the celtic league

America (F yeah) is a massive powerhouse with any ideology, but where it can really do some overpowered things is with its sworn enemy C O M M U N I S M. If you liberate yourself early game on something like Bermuda to switch your ideology fast, this can bring some major problems due to the modifier it gives you for the next in-game year (Forced Regime Change). However, if you change immediately to Communism from Cuba, and then enact the 'Forced Labor For Dissidents' policy, this negates the debuffs to your factory and resource outputs. And America can (Tested this myself) survive without major stability loss from the modifier as well, thanks to Communism's stability boost, as well as putting on low taxes and low government spending.

You would need to build actually less factories to upkeep America during the modifier's duration, however you still need to buy the resources to upkeep them, since the FLFD policy only makes you break even on resource production. So buy the basic resources you need and wait a year for your tax money to return and you have what could likely be the most overpowered nation in the game.

(This, along with my other 'best' thoughts came from me eating Italian food with steak.)