What factor best explains the rising population and importance of New Orleans during the 1800s?

The rising population and importance of New Orleans during the 1800s can best be attributed to its strategic geographical location, which is characterized by being situated at the mouth of the Mississippi River. This location provided the city with significant advantages for trade and transportation. As one of the busiest ports in the United States during that period, it became a central hub for the movement of goods, primarily agricultural products from the interior of the country and imports from international markets.

The proximity to the river allowed for easier access to shipping routes, which facilitated trade not only locally but also with international partners. Additionally, the city served as a cultural and economic gateway, attracting immigrants and settlers who contributed to its population growth and economic development. This combination of maritime access and its position as a commercial center greatly influenced New Orleans' importance and its demographic expansion through the 19th century.

Other factors, such as an oil industry or significant infrastructure investments, were not predominant influences on New Orleans’ growth during that specific era. Therefore, the oceanside location near a large river system is the most compelling reason for the city's rise.