How long does animus last between nationalities after the original friction that caused the animus ceases?
This question is germane because first world nations are importing peoples from war ravaged nations in gross lots. Many of these immigrants bear deep animus in their hearts, not gratitude.
My maternal grandmother's family left Ireland in approximately 1850. My grandmother was born in the 1890s and died in the 1974. Until the day she died she carried a deep anger against the British.
Let me do the math for you: 1974-1848 (middle year of the potato famine) = six generations.
Anecdotal data is limited because of sample size. Is there a better way to measure animus over time?
One way would be via first names.
Let us speculate that Anglophiles are more likely to name their children after British royalty: Names like Edward, Philip, Charles, William, Harold/Harry, Victoria, Elizabeth, Kathrine/Kate, Diana. Let us also speculate that those who bear the British animus are less like to use those names.
The Social Security Administration publishes annual lists of how popular any given first name is.
The test of how quickly animus wanes would be to compare the rate of "Royal names" for mother's whose last name starts with "Mc" or "O'" as a percentage of the US population's base rate.
If the percentage of "Royal family" names in Mc-O' families exceeds some arbitrary floor, say 70%, then one can conclude that the level of animus can "hide" in the general population. A reason to use a arbitrary floor is because of the tendency for people to name children after ancestors. If nobody in your family from your parent's generation was named "Elizabeth" then you are less likely to choose that name for your child.
That would be an interesting study and it would give us a sense of how many generations it will take for refugees who currently blame the US (or Britain or the EU) for bombing/strife that forced them out of their homeland to assimilate.