The federal government needed to regulate the settlement of western lands to
secure the land for native americans
valse revenue to pay off its debts
increase the number of slave states
prevent european nations from buying the land

The federal government needed to regulate the settlement of western lands to "prevent European nations from buying the land".

Option D

Explanation:

Abraham Lincoln, the president was signed The Homestead Act on 20 May 1862. On 1 January 1863, under this act Daniel Freeman did the very first claim. As that offered public lands for residents or future citizens upto 160 acres.

Hence, provided them to live on it, develop it, and pay a small registration fee.  The government granted over 270 million acres of land while the legislation was in force, therefore such actions prevented Europeans to acquire land.

C) to gain free trade along the pacific coast

Explanation

US expansionists wanted California to thwart British ambitions in the area and gain a port on the pacific ocean