The majority of Asian Americans today are immigrants. Most of them are here thanks to groundbreaking changes in US immigration law implemented with the Immigration and Nationality Act of 1965 (the Hart-Cellar Act), which lifted the national origins quota system that had been in place since 1924. The Immigration and Nationality Act (INA) was first passed in 1952 in order to centralize US immigration and naturalization laws, and provide a systematic recodification. This act was also enormously significant because it removed all racial barriers to immigration and naturalization and furthermore rectified gender discrimination by granting husbands of US citizens the same preference as wives. It was not until 1965, however, that the national origins quota system was removed, finally putting Asian immigrants on an equal footing with immigrants from Europe. The Immigration and Nationality Act of 1965 is thus considered landmark civil rights legislation.
The Hart-Cellar Act replaced the national origins quota system with a new preference system that privileged family reunification and skilled workers. Preference was given to the family members of US citizens and permanent residents. In addition, preferences were created for highly skilled professionals, especially in the science, technology, and medical fields. Such professionals were highly sought after at the time in order to enhance American competitiveness during the Cold War era. The immigration reform of 1965 promoted the migration of large numbers of highly educated and skilled Asian professionals to the US, a phenomenon sometimes known as the "brain drain," and profoundly shaped the characteristics of the Asian American population today. What connection can you see between the passage of this immigration reform and the emergence of the "model minority" stereotype of Asian Americans?
Here is an official timeline to US immigration law in the post-World War II era.