'Their good fortune was partly due to the help of the Wampanoag Indians, who had taught the pilgrims how to grow various native crops. To this day the tribe reminds North Americans that its subsequent persecution was more than ungrateful.'

The fourth Thursday in November is Thanksgiving Day in the United States. For those on the eastern side of the Atlantic, or those in the States who have forgotten - what's it all about? By Andrew Chapman

Thanksgiving is associated with harvest - celebrated in Britain when the wheat has been cut and the apples picked. Many countries around the world celebrate harvest in one way or another.

In Canada, it has been celebrated on the second Monday in October sincer 1957, and on other dates as a national holiday since 1879.

The tradition is said informally to date all the way back to the 16th century, when Martin Frobisher held a ceremony in Newfoundland.

In the United States, the celebration of thanksgiving is generally held to have started in 1621 - after a poor harvest in the year of their arrival (1620), the Pilgrim Fathers fared better in the following year, and gave thanks to God.

Their good fortune was partly due to the help of the Wampanoag Indians, who had taught the pilgrims how to grow various native crops.

To this day the tribe reminds North Americans that its subsequent persecution was more than ungrateful.

George Washington and subsequent Presidents of the United States celebrated thanksgiving ceremonies in various years over the next couple of centuries, but it was Abraham Lincoln who declared it an annual feast, in 1863 - to be the last Thursday in the month.

This was partly to cheer the nation up after the American Revolution.

In 1939, President Roosevelt moved the festival to the penultimate Thursday of November, to give retailers more time to market their wares for Christmas.

Two years later, a ruling by Congress reached a compromise: the fourth Thursday of the year, still observed today.

Thanksgiving has become associated with a number of particular dishes, including turkey and pumpkin pie.

Many of these traditions date from the late 19th century. Many modern prayers acknowledge the debt modern society owes to those less well off, both in the past and the present - thanksgiving today embraces a complex range of issues.