In November 1863, President Lincoln made Thanksgiving Day (up till then rather unofficial and only vaguely celebrated) a National Holiday, inviting his "fellow citizens in every part of the United States, and also those who are at sea and those who are sojourning in foreign lands, to set apart and observe the last Thursday of November next, as a day of Thanksgiving and Praise to our beneficent Father who dwelleth in the Heavens."

As an American sojourning abroad, Thanksgiving has always been a bit difficult to explain. If asked, most Americans would mention pilgrims and native Americans - because that is what we learned in school. The mythology goes: the pilgrims at Plymouth survived a long and arduous winter in their rather poorly chosen location because the local Wampanoag, among them Squanto, taught them how to grow corn and fish for eels, among other essential survival skills. A feast was had to celebrate this neighbourliness and give thanks to God that everyone made it through. And that was the first Thanksgiving.

As schoolchildren, we commemorated this story by making little pilgrim collars and feathered hats (yes, really) out of construction paper. That all seems a bit trivial now, more about a safe America we fantasise about rather than the complicated America we have - and always have had.

One feast becomes a tradition only over time, and Thanksgiving was celebrated haphazardly throughout the United States up until the Civil War, with different states observing some sort of semi-religious feast at different times.

When Lincoln asked his citizens to take pause, it was only three months after 50,000 people died, on both sides, in a three day period at Gettysburg. Notably, he asked Americans not just to reflect and give thanks for their "singular deliverances and blessings," of the past year but also to have "humble penitence for our national perverseness and disobedience." You have much to be thankful for, Lincoln reminded us, but there is much to regret - and much to get done, "to heal the wounds of the nation and to restore it ... to the full enjoyment of peace, harmony, tranquility and Union."

There is much to regret. There is much to be done. This is Thanksgiving. Its history - like our history - is not something you would find in a storybook (and there are no convenient costumes) but is borne out of the best hopes of our dark, divided heart.