What are the four causes of imperialism?

It is very difficult to identify the actual cause of the new imperialism of the 19th century. However, economic factor is considered to be the most important one provoking imperialist expansionism.

First, it is said that the most important factor in imperialism was investment.

Second, another opinion regarding imperialism is that imperialism was a nationalistic, not an economic phenomenon.

Third, considerations of national prestige played a large part in the story of imperialism. It was thought that to be a great nation one must colonize.

Fourth, sometimes Social Darwinism was projected as a factor behind imperialism. It viewed relations between states as a perpetual struggle for existence in which only the strongest survive.