What was the biggest motivating factor in moving westward in the 1820s and 1830s?

The swelling American population played a large part in the decision Americans made to head west. According to America’s second census in 1800, the U. S. population numbered 5.3 million. By the seventh census, in 1850, the population had quadrupled to 23.2 million. It’s been estimated that between 1820 and 1850, four million Americans moved west. In the first half of the 19th century especially, Americans were mainly farmers who needed arable land for their crops and livestock, land that was not available in the overcrowded and farmed-out east. There were, as well, financial panics (in 1818 and 1839) that uprooted people and sent them west seeking a fresh start.