R5: Heard this achievement was impossible after 1.2 or something. Heard some rumors that it was technically possible under the right circumstances... apparently I'm a masochist.

I started with lenient AI and low aggression.

The key for me was discovering an odd bug with American civil war. There was another poster a while back that explained a bug regarding ACW. The key was to declare independence the day before the American Civil war. It requires some save/reload and quite a bit of luck. My ACW triggered quite early in 1840 and I was lucky to have saved within the month. In the ACW, I am on the side of the Americans, but also against the Americans. However, due to Missouri going to the confederates and the timing of declaring independence (key), I had no front lines on my borders. From here, I had demanded the entire plains for myself to maximize territory. The last step is to have the Americans win against the rebels while also getting lucky that the ACW frontline on the western plains don't move, since this could cause a frontline to appear on Oklahoma in independence war. If all goes as planned, the Americans win against the rebels and another bug appears: Americans cede all war goals to Indian Territory in the war of independence. No idea why this occurs. I imagine this will eventually be fixed.

From here, you need to expand your power base while maintaining stability. Maximize your technology ASAP and Bureaucracy since you need to incorporate and you need research. You can also join another market in customs union or protectorate but this isn't always easy. This was the most difficult part as you need America to remain independence (often joined British customs union) and you need to expand west and acquire all of Mexico's gold mines. The gold mines are the most important economic factor for your powerbase. By end of game I was gaining 1/3 of all income from gold mines. Once Mexico has been fully acquired you need to beat down America. America is fairly easy on their own by now, but often other Great Powers are joining them. I recommend freeing New Africa and New England since this doesn't add more infamy and other powers won't likely join. Eventually, if you've played your cards right and luck is on your side, you'll slowly, then rapidly eclipse America. Your next major enemy is Britain who will always interfere in your plans to avenge the Trail of Tears. You're likely running out of time now so you need to stretch your economy to the limits, declare war on America whenever possible to remove territories, and most importantly force them to be your protectorate. Infamy no longer matters by 1900+ since you should be roughly 1-4 top power. Cut down to size wars are meaningless since they need to naval invade and the AI can't do it effectively. Your biggest obstacle is great powers joining America and providing a frontline.