This graphic highlights the enormous shift in immigration patterns into the US from pre-WWII to post-WWII. If you go to the source (here), the graph becomes interactive, showing actual numbers by country and by decade as you mover cursor over the graph.
Note that these are total numbers. As a percentage of the total population, immigratin is considerably less than it was in the 1920s. Note, too, that immigration dipped when there were sizable economic downturns.
Wouldn't it be interesting to see something like this for Canada! (or other countries, for that matter)