Economic gains were certainly one of the primary motivators behind 19th Century imperialism. Vladimir Lenin would likely agree with this assertion as well. As industrialization and the mass-production of goods increased throughout Europe, industries were forced to look elsewhere to sustain financial/economic growth for their expanding enterprises. Foreign lands offered countries the best means to expand their industrial output via trade and allowed for the development of foreign (cheap) labor.
Although many countries claimed that their imperial endeavors were noble in practice (i.e. to civilize the so-called savages and barbarians of foreign lands), the competition to have the largest empire (in terms of land) was also a major motivator for the European countries of this period.