Imperialism is the policy of extending political and economic control over a weak country by a powerful one. The phenomena gained strength in the nineteenth century AD, largely due to the Industrial Revolution.
You have read that the Industrial Revolution led to a tremendous increase in the production of goods. A market for these manufactured goods and sources for obtaining cheap raw materials for producing more goods were desperately needed. Areas to invest surplus capital were also required. This led the European nations to acquire colonies in the politically and militarily weak countries of Asia and Africa. These countries could easily be conquered by the powerful Europeans. They provided a good opportunity for the investment of surplus capital. Besides, Asia and Africa were well provided with natural resources and had a huge potential to absorb finished goods.
India, too, experienced the evils of imperialism. Britain made India its colony and economically exploited it for its own benefit. The struggle of the Indian people against imperialism ended in AD 1947, when India became independent.