In the beginning, America obtained vast territories.
To prevent those territories from being settled, then claimed by foreign powers, America needed to seed those terriories with settlers as quickly as possible--so America imported people, rather than wait generations for our population to increase and migrate.
And somewhere in all this, big landowners profited (as they do today).
After the abolition of slavery (which also drove the price of paid labor down among poor whites), the industrial revolution in America needed cheap paid labor, so they flooded the country with immigrants to increase the supply of paid labor, thereby driving-down wages.
Immigration has always served certain interests, while hurting other interests.
Today, immigration is used to keep the cost of labor down while also dividing and conquering the American population through diversity ("they" don't want one, large, dominant culture with a belief system that gets in "their" way).
All this serves the powerful.
and there's plenty of country left.
Were there plenty of country left, why is the price of real estate rising?
If there is plenty of country left, why do we need pollution conttrol, recycling, and water-saving toilets and showers?
And as the number of voters approaches infinity, the power of your vote approaches zero.