What were the pressures on the United States government to push for expansion?

The major reasons that fueled a desire by the US government to seek to expand was an ever increasing population due to migration into the country and secondly the US looked to gain more Territory as a way of gaining more power to withstand any offensive approach from any of its enemies.

The nation was consumed by its struggle to maintain its neutrality in the face of threats from Britain and France.

Explanation:

One other major reason that fueled the US to expand was a desire to free other less civilized regions from the oppression of European monarchies.

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.