Any foreign national who wishes to relocate to any other country, on a permanent basis need an immigration visa or in general terms called a PR (permanent residency) of a particular country.
There are many reasons why any person wishes to immigrate to a different country. Some of the basic reason are Financially secure future, High Standard of living, Better education, Better work opportunities, Political reasons, Change of scenery, and also due to their partner or soul mate who lives in a different country. Apart from these major reasons there are many other reasons why anyone would emigrate.