Is America headed towards becoming a 3rd world country?

The U.S. is no longer a melting pot. Other people emigrate here and bring their culture with them. The largest growing segment of the U.S. population is from a certain third-world country. Third-world culture is being brought here quite literally by the truckload. It will only be a matter of time until they outnumber the rest, and then our culture will be their culture. Invasion historically has always resulted in the loss of the original culture, replaced by the new (in this case, third-world) culture.