What factors promoted America's search for new markets?

Beginnings of American
Imperialism:

The following information will not exactly
answer your question, but it will give you information which will help you compose your
answer.

Southern observers foresaw before the American
Civil War that northern industrialists desired to absorb Central America and the
Carribean. Southern observers said that northern industrialists intended first to
exclude slavery from the territories of the United States so that states could be
established whose U.S. Senators would not oppose the tariffs and improvements of harbors
and construction of railroads at taxpayers’ expense for the industrialists’ benefit.
When they had a Constitutional majority (3/4 of the whole) of states under the control
of pro-industrialist governments, they would pass a Constitutional amendment to abolish
slavery in the states. Abolishing slavery would bankrupt the southern plantation owners.
Northern industrialists would buy the plantations dirt-cheap, establish peonage to work
them, and export the excess former slaves to northern factories for cheap industrial
labor. They would then absorb Mexico, Central America, and the Carribean and establish
peonage in all of these areas to raise coffee, cotton, tobacco, and sugar, for supply of
their northern factories.

An article describing this
process was published in DeBow’s Review issue of February
1857.

What actually happened was little different than this
prediction. Slavery was forbidden in the territories; a Constitutional amendment was
made to abolish slavery in the states; cheap labor in the form of ex-slaves and cheap
land in the South became available to northern industrial interests; the new industrial
America partly absorbed and partly dominated the Carribean; Central America was
dominated without being absorbed; the Philippines, Hawaii, and several central Pacific
islands were absorbed; a big hunk of China was dominated. All, that had been predicted,
took place, and more.