Wichita Boy:

As Fresh Air notes, the American Revolution was fought among a populace that was roughly one-third in favor of independence, one-third opposed, and one-third fence-sitters.

After the founding of the US, the War of 1812 was incredibly unpopular, especially once the Brits blockaded American ports. IIRC, this resulted in the first arguments for secession, ironically by New England, in the “Hartford Convention,” in which they wanted to preserve states’ rights against the perceived tyranny of James Madison.

However, your larger point, that most American wars have been fought in the context of far less unity, is absolutely dead-on. World War II was the outlier, not the norm.