Imperialism refers to gaining power and dominion over other peoples and nations by means of colonizing them. This can be done by force, deceit or economical pressure designed to subjugate the colonized.
This was the driving doctrine that drove the Europeans to establish colonies around the world from the 16th to the 20th century from North America in the west to Australia in the east.
Colonization was done so much that a significant amount of the world fell under colonization such that the British empire at some point, controlled 24% of the world as we know it today.
They justified it in part like the French Premier, Jules Ferry by saying that they were doing it to civilise the world and its so called 'inferior' races.
It was supposed to prevent the export of cotton and smuggling of war materials into the confederacy. The confederacy constructed torpedo boats to try and get around it.
