Some interesting excepts from an article on Thanksgiving a reader helped me find (thanks to DG):

By having Lincoln as its midwife, Thanksgiving also celebrated the blessings of American nationhood as well as its domestic ideals. Thanksgiving was – and is – a holiday of American civil religion, that is, religious belief in the national purpose and destiny. The nation, it was believed, was blessed by God and given a special purpose in the world.(14) (The distinction between Thanksgiving and Christmas in this regard is a matter of degree rather than of kind, since some Victorian Christmas trees in America might be decorated with the American flag and those in Britain were draped with the Union Jack.)

Also, Thanksgiving, was -and is – used as a tool to enhance faith in the American civil religion as described above:

Even before that, the festival of the home had become the dominant way of celebrating Thanksgiving. In the Progressive era Thanksgiving acquired a new meaning, as a domestic occasion that incorporated newcomers into American customs. Surveys of elementary school principals in the 1920s show that Thanksgiving was the most frequently celebrated holiday in the schools, even slightly edging out Christmas.(35) Public school teachers and settlement house workers hoped to assimilate immigrant children to America and use children as Americanizers of their parents. They wanted the children to become patriotic citizens who demonstrated their love of country through celebration of cherished American holidays. Hale helped to invent a domestic occasion, which emphasized family homecoming; Lincoln saw in the holiday an opportunity for a nation to give thanks for its blessings. Both of them used the language of civil religion, even though in the mid-nineteenth century the public still understood the holiday as a Protestant one. In the Progressive era teachers did not emphasize the Protestant origins or meaning of thanksgiving, and instead portrayed the holiday in secular, nationalist terms, as a day when all Americans could feel they belonged to the nation.

And this part:

The schools recognized that they had to develop an emotional bond between the immigrant and the nation, a love of country. Immigrant children could be taught American history and learn about the holidays, but the home was where the deepest feelings of patriotism were conveyed.(42) Thus, the home celebration of holidays needed to be encouraged to reinforce the patriotism learned in the school. By holding a feast around a common table, an immigrant family could demonstrate its acceptance of American customs and knowledge of American history.

And I thought this was interesting:

The Catholic church opposed the holiday as a Protestant rite as late as the 1880s. Many in the South still thought of Thanksgiving as a Yankee day.(44) In the West the day was largely one for hunting, and the feast could be a brief and unassuming one.

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