Economy: Imperial governments and companies under those governments were doing whatever it took to maximize their profits. Their expansion, slavery and many other terrible practices were done repeatedly as a way to stay rich, but also not to stay behind other imperialists.
Ethnocentric: Many times, Europeans just believed to be superior and entitled to the rest of the world.
Religious: Because of the amazingly powerful influence of the catholic church in Europe, imperialism was also used as an excuse (or vice versa) for Jesuits to take the word of god to other peoples.
