What were the pressures on the united states government to push for expansion?

1. Free land

2. Mexico was not strong enough to hold back the American invaders.

3. Immigrants from Europe wanted land.

4. Population growth fueled the need for more land.  

5. The USA wanted to grow and become a more powerful and significant country at the expense of Mexico, Canada and the Indians.

Explanation:

president thomas jefferson commissioned the expedition shortly after the louisiana purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an american presence in this territory before britain and other european powers