Two of the most significant factors in the spread and increase of cotton agriculture across the South and West of the United States during the first half of the nineteenth century were:

The availability of the Louisiana Territory and the discovery of cotton gin.

Explanation:

The increase in the supply of cotton in the south and western parts of the united states was possible due to the development of the Louisiana territory which was a large organized territory. It stretched from the Gulf of Mexico and was developed for economic profits and boosting trade. The invention of the cotton grin also helped in the spreading of cotton use.