EAD cards, popularly known as work permits, usually expire after a year, but the length of time may differ in some situations. Learn more about EADs here.
In the United States, permanent residents and naturalized citizens have similar rights in so far as being able to legally live and work in the country. http://www.ksvisalaw.com/citizen-versus-permanent-resident/
Immigration to the United States has been a hot-button political issue. To begin to understand immigration in this country, immigration lawyers in San Diego look at the underlying reasons. http://www.ksvisalaw.com/reasons-people-immigrate-to-the-united-states/
Various circumstances can motivate you to move from one country to settle in another country permanently or temporary, details are here http://www.ksvisalaw.com/