A case can be made as early as 1848, when a peace treaty with Mexico was signed giving the US huge pieces of territory claimed to be owned by Mexico. In this situation, both countries can be said to have had imperial ambitions. The territory claimed by Mexico was the land the Spanish previously "stole" from Native Americans.
the world
Greed
The following countries were at one time, under US control:PhilippinesCubaNicaraguaMexico (Veracruz)HaitiDominican RepublicJapan (various islands)United Kingdom (Falkland Islands)Denmark (Greenland)IcelandAustriaGermanySouth KoreaIraqFrance (Clipperton Island)Marshall IslandsMicronesiaPalauIncludes countries with US occupations.
First fur trade millionaire was J J Astor See Wikipedia "Fur Trade"
South Carolina was the first Southern state to secede, on December 20, 1860. (see related question)
the world
It didn't imperialize China.
It seems as though Great Britain is unable to imperialize the world, after all.
India -- Gandhi's period. Africa -- read Things Fall Apart.
Italy tried to imperialize Ethiopia. When the Italian people tried to conquer it, they were defeated because the Ethiopians were prepared.
Greed
they wanted to.
the portuguese
Most nations imperialize or colonize in order to gain the resources of the other nation. Usually, one nation will not colonize another if that nation will fight against it.
because they had it coming! jk. i love the Philippines
because they need to take their natural resources
because he discovered diamonds and gold and helped imperialize africa