My uncle was arguing with me that during his childhood (1960s and 70s in a suburb of Boston), the swastika was a symbol of Germany. He claimed that there was no anti-Semitic connotation or usage as a symbol of hatred or white supremacy at that time.
I (26 years old) find this hard to believe, since I've always associated the swastika with the Holocaust and have always known it as a cultural taboo, if not hate speech.
Was the swastika a symbol of white supremacy and racial hatred in the decades following WWII or is this a more recent development?
The swastika and sauvastika, like the cross and the circle with a dot, are really simple doodles. As such they were invented over and over and used on ceramics or scraped into rocks as simple decorations. In these instances, they don't really symbolize anything.
Over time, as societies became more complex, they began assigning some level of meaning to these doodles. In India, the swastika & sauvastika stood for thunder and lightning, while in China it was more a generalized "good luck" symbol. Similarly, the circle with the dot might be an anti-evil-eye eye, or stand for the sun, or the horizon all around with the viewer in the center, and thus the earth. These meanings are not inherent in the symbols, so they can be different in different cultures and over time.
Our modern concepts of race and racism developed in the 1800's, so we should not be surprised to find racist groups appropriating symbols. One of these was the swastika, that was taken to represent the white Aryan race before cultural and racial dilution by the Mediterranean race or the Slavs. It was chosen to be not-Christian and pre-Christian, reaching into the pagan past before Jewish corruption via Christianity.
Anti-Semitism was rife in Europe, and had been for centuries. Check the Dreyfus Affair. This was frequently interwoven with Aryan supremacy back in the 1880s.one reason to choose the swastika is its association with the Aryans of Vedic India.
So this became a common way to mark "I am an Aryanist" all over Europe: Scandinavia, France, the Low Countries, Germany, Austria, &c. Hitler grew up with this as a symbol, as did most of the Nazi elite. When they came to choose a symbol for a racist Aryan party, the swastika was a natural choice.
Only when the Nazis came to power did the swastika become a symbol for Germany - Nazi Germany. If you look at military iconography on aircraft and uniforms of Germany in the First World War, or any earlier Prussian/German state, you will see the Knight's Cross, the Iron Cross, the Blue Max and other forms of simple cross, but no swastikas, no bent crosses.
In short, your uncle is so far off he isn't even wrong. In the Sixties and Seventies, every time the media used a swastika it was shorthand for Nazis, evil villains in cheap thrillers, the Holocaust, and anti-Semitism. Check the cover of The Boys from Brazil (1976) which signals "Nazis!" With a small swastika.