The term mouse fly is kind of a contradiction and one of the types of flies that brings the word fly in fly fishing almost as far away from something flying as possible - still surpassed by shrimp flies not to mention crab flies, but anyway...
One of the reasons Britain became rich was because the Industrial Revolution (factories and such) got off the ground there sooner. Britain had a large navy, and many colonies in other parts of the world, such as India, and Rhodesia.
There are two main ways in which the Industrial Revolution and imperialism were linked to one another. First, the Industrial Revolution made imperialism more necessary. Second, it made imperialism more possible. The Industrial Revolution helped to create a situation in which the European countries (as well as the United States and, eventually, Japan) felt that they needed to have large empires.