Avi > Americans have only been intermarrying in large numbers in the last couple of decades
Pew says intermarriage was 17% before 1970, big jump to 35% in 1970 and then gradual growth to current 58% This is a little biased as asked in 2013 about marriages that existed that long .. and also at some point numbers become meaningless as those who are counted as “Jewish” actually are not.
other stats I found. Looks like Russians rates grew earlier than in US, but in Ukraine about same time
Germany 1900s: 20%
USSR:
1924: Russia Males 17% Females 9% (talk about shidduch crisis!) Ukraine 4%/5% Belarus 2%/3%
1936: 44% 35% 18%/16% 13%/11%
1978 59/ 43 45/34 38/26
1988 73/63 54/45 48/40