OK, I got through and started playing. After toying with some tutorials and restartign to experiment, I managed to do the following playing as the U.S.
Defeat Mexico, annex Texas and everything clear to California, and also Chihuaha. I colonized Canada, and then the rest of the continent. I killed off my hugely expensive, utterly useless Navy.* I bowed to British pressure to disarm the first time, went to war. I prioritized techs (Medicine -> whatver I needed for Manifest Destiny -> economic techs for railroads and such -> Culture techs for prestige and improved research/education.
*My Navy cost more than all my soldiers combined. It costs mroe than a huge army of enough size to squash all the South in two years.
However, England will NOT leave me alone. They keep declaring war, which keeps from doing anything actively. This isn’t so bad, except that I don’t see how I can keep them from it and I can’t do much warscore just in Canada. Worse yet, the AI seems very up-and-down. Sometimes they’re unstoppable and do way more damage than in reasonable under strange circumstances, managing to outnumber me 2-1 with troops they pull from Hammerspace.
So can someone explain a bit how I can manage wars better. Mexico was one thing, but England is another. Am I making a mistake by focusing on sieges, or should I just concentrate my troops, mash their armies, retreat to regenerate my numbers, and so on? I’ve currently got an army rating of about 73, but the attrition rate is painful and the British somehow manage to inflict triple casualties on me. What am I missing (I did pick up Muzzle-loaders, but am not up to Breachloaders yet; it’s only 1865!)