Imperialism has been common practice around the world for many centuries. It is a practice of growing a country's power and rule over other countries through militaristic, political, or economic means. Some examples of imperialistic behavior are Nazi Germany's invasion of Poland in 1939, America's invasion of Vietnam in the 1960s, and Britain's rule over India for hundreds of years from 1700 to 1900. Quite simply, imperialism is about building up empires. The benefits of imperialism fall into two broad categories: self-preservation and discovery (obviously, wealth increases, too, but that doesn't seem to be unique to imperialism, as any country or empire could increase its wealth without imperialism). When a nation engages in imperialistic behaviors, it can ensure that its civilization survives throughout history and also discover new ideas, inventions, and resources in other lands.
Of course, the drawbacks to imperialism are the death, destruction, and oppression that often accompanies any kind of power grab. Any discussion of examples, such as those mentioned above in Poland, Vietnam, and India, is incomplete without mentioning the negative impacts of imperialism. Militaristic behaviors are never clean, and deaths do happen. Destruction of private and public property is inevitable in any type of take over, whether it be from war or from resistance riots. Also, oftentimes people are subjected to the ruling powers of the country that is doing the taking over, which is oppressive, cruel, and dehumanizing. Customs, cultures, and religious beliefs of the victims are usually ignored and even offended.
Overall, imperialism has hurt the world in terms of net impact. There are much healthier and beneficial ways to increase wealth and power of nations, such as by free and fair trade, tourism, production, and governmental programs. Imperialism is viewed negatively in general nowadays, such as when a politician accuses another politician of being an imperialist in a campaign. Imperialism is not an ideal that civilized and developed nations value in general.