This is an important question.
The 70s and 80s experienced an influx of immigrants from Asia and Africa with the passing of the Hart-Cellar Act in 1965. President Lyndon Johnson did away with the racially oriented quota system. This act was in response to the civil rights movement. When this act was passed it was thought that immigration would come from traditional European countries, but people from Asia and Africa came (Korea, China, India, Philippines, to name a few).
The Hart-Cellar Act allowed people with families here to invite other family members to come to America. Also people with various skills were also allowed to come.
Another important act that was passed was the Immigration Reform and Control Act in 1986. This act gave over a million illegal workers amnesty. Some argue that the number was actually higher.
These acts have made America much more diverse and multicultural. Moreover, many of the people who immigrated in the 70s also came with various skill sets, which made them upwardly mobile. In light of this, these acts created a far more diverse country also in terms of economics.