How long did it take Americans to lose our English accents?

by MrSaucyNips

Basically, once we Americans began to come to what is now the US, how long did it take is to evolve to our current dialect? I've noticed a lot of movies that take place during the Revolutionary War and even Civil War are split between us still having a somewhat English accent, or sounding basically like the Americans we do now

the_howling_cow