Right.
Unfortunately, in 1819, the United States goes bankrupt attempting to keep pace with the building program of the richest empire on Earth. Congress, having begun to make aristocratic appointments(like Admiral) in the midst of the economic collapse, finds a number of members tarred and feathered while in their home districts. The nation teeters on the brink of dissolution until 1822.
In 1832, a small effort begins to rebuild the Navy, under cover of calling the vessels "revenue cutters". A sufficent force is accrued, despite the Panic of 1837, to support the U.S. war with Mexico in 1846. Emboldened by this success the American Congress again embarks on a hare-brained scheme to match the Royal Navy. In 1857 the cost of this idiotic effort, coupled with the economic downturn of 1857 (which, by itself, would have been suvivable) fractures the already fragile Union, this time permanently.
By 1874 the Former United States is home to no less than five separate nations, which engage in intercene warfare with shifting alliances both on the North American continent and with European states. Without the Monroe Doctrine, European countries embark on a massive retrenchment across the Western Hemisphere, starting with Napolean III's successful takeover of Mexico.
NAVIES are EXPENSIVE. One of the things that is consistently forgotten in these thread is that the United States was NOT a rich country in the early 1800's. Even with the fairly small, albeit well designed, fleet that the U.S. was able to construct IOTL, the Navy Department was annually the largest single line item in the American budget, with defense spending sometimes approaching 40% of the total American Government Budget in some years. Where would the money come from for this stunning building program?