It would be more accurate to describe the waiting list for family-sponsored immigrants as 14 different queues moving at different speeds.
Currently, there is only one queue for the spouses and minor children of permanent residents (“F2A” visas), no matter where in the world they were born.
But all of the other green card categories have two or three extra queues, because of country-based caps. (For decades, no single country of origin has been allowed to account for more than 7% of all family-preference and employer-preference green cards combined.)
This means, for example, that Indian, Mexican, and Filipino siblings of U.S. citizens each wait in their own separate queue, while siblings from all other countries wait in another (faster) queue.
Here is a view of the 14 queues based on how many people are waiting in each of them and how many just got their green cards last year:
Learn more in our 2019 family-based immigration report.