If we are a rich and powerful country, then preserving the country would most likely mean remaining richer and more powerful than some other countries.
But it's not all about materialistic factors. Patriotism also plays a big role.
That was certainly true in 19th century America, which may have been destined to play a big role in the wider world, but wasn't doing it yet.
All societies, ancient or modern, have either rigid or implied caste systems. Warriors (kings) are always the top echelon, with priests running second. It is the responsibility of the intelligentsia - as represented by the shamans - to sell the virtues of war to the masses. It's actually quite easy: they simply appeal to patriotism.
Samuel Johnson coined the famous phrase "Patriotism is the last refuge of scoundrels". However, most do not realize he had this to say about our country's founders in 1777: "How is that we hear the loudest yelps for liberty among the drivers of negroes (sic)?" (Page 364, Life of Johnson; Boswell)
You and I are on the same side. I just advocate considering more than rote, surface level sentiment to discover historical drivers.