History of Thanksgiving. This is a brief history of Thanksgiving type of celebrations around the world. It also covers the roles of two American Presidents (Lincoln and FDR) in establishing the holiday in the United States of America.
From the site:
Since the autumn harvest usually occurred sometime between late September and the middle of October, the colonists' harvest festival wasn't celebrated in November, like it is today. For hundreds of years, people simply celebrated the harvest whenever nature was ready. In 1863, President Lincoln declared the last Thursday in November as Thanksgiving Day. However, since he did not establish it as a national holiday each state had the right to decide when it would celebrate Thanksgiving. It wasn't until 1941 that Thanksgiving was declared a national holiday, by President Franklin D. Roosevelt.