Question

How significant was Manifest Destiny in shaping government policy and people's attitudes and actions between 1780 and 1860?

Answer 1

It promoted the migration west and provided an ideological justification for the war with Mexico between 1845 and 1849.

Explanation:

You can find more information here:What is the definition of Manifest Destiny?

Manifest Destiny was only a ideological trick to justify the conquest of the West, the real motives were economic as the West provided more lands and thus more resources.

The Gold Rush in 1848 is one of the best examples of that trend.