I am heavily abusing naval invasion mechanics and how they absolutely brainfuck the AI. I still almost lost this last war (liberating New Africa and taking Pennsylvania) because Great Britain's idiot fleets were set to "defend naval invasions" and wouldn't help me
Ok so I managed to do it in 2 wars, first was Mex+Fra vs US+UK, I lost but only 2 states with 0 buildings, by the next war I also had a defensive pact with Russia and managed to win, In the next 2 wars I should be able to get all of USA.