On November 26, 1863, President Abraham Lincoln declared the last Thursday in November would be a day of giving thanks. This proclamation was made during the Civil War. Lincoln wanted a national day of recognition to give thanks for the Union army and its crucial victory at Gettysburg.
George Washington also held a national day of giving thanks and prayer but it was not made into a national holiday. Those against the holiday stated it was inappropriate to celebrate a day of prayer in a country that separated church and state.
President Roosevelt moved the holiday to the third Thursday of November to give stores a few more selling days between Thanksgiving and Christmas. Congress stepped in and urged him to move the holiday back to the fourth Thursday of November; he conceded, and as of 2014, this remains the date Thanksgiving is celebrated each year.