To be honest it started before 1965. By then whites had already been reduced to 85% of the population, the place where Britain is today. America started off with a huge negroid population which thanks to Christian cuckoldry was never repatriated or sterilized. At least Hitler had the sanity to sterilize all Afro-Germans(around half a million) i.e mulattos after coming to power. Thanks to that, there aren't 6 million negros in Germany today. France brought in negroes after WW1 and now they're drowning in it.

And then after ww2, the mexican flood had already started. US capitalists could not get enough of it for cheap agricultural and construction labor. After 1965 the floodgates were fully thrown open. The border with Mexico essentially stopped existing for all practical purposes and the endless flood began.

https://en.wikipedia.org/wiki/Mexican_Americans

Today there are just 36 million Mexicans alone in the US, then there was the huge flood of Peurto Ricans and Cubans during the cold war and beyond.

But by far the most decisive cause in reducing white American majority, has been low birth rates. Any society that liberates women will soon find them in this spot. Abortion, birth control, women in the workplace and sexual ''liberation'' gutted the white birth rate and contributed to white decline more than anything

Capitalism more than anything contributed to the downfall of America and Western civilization. The worship of money and the relegation of tradition to the art gallery. Even today Capitalists lobby for mass migration despite the mass unemployment crisis and it was Capitalism that pushed feminism and abortion on the population. Its happening in Japan as we speak and it will take very little for the plutocray to flip it demographically owing to its old population