Awesome viz! Would like some perspective on the overall volume, too. Maybe add a bar chart above the timeline/slider showing total immigration in each year? Maybe even alongside a graph of total US population growth so it's clear how much of the growth is due to immigration.
Also don’t forget emigration. I don’t know the numbers for the US but for example in the EU some countries had more emigrants than immigrants during some years (e.g. Spain in 2010).
