Commonly, we say that the Nazis adopted the Indian swastika, but today I understood that apparently they took it from the people of Troy in the aftermath of discovery of the German archaeologist Heinrich Schliemann, 1822-1890 who found Troy in his excavations in Turkey. He made a connection between swastikas from Germany Troy and Iran in the frame of the Arian racial doctrine in his book:
Schliemann, Heinrich , Troy and its remains, London: Murray, 1875
In the above picture, we see ceramic disks from this book. These disks are dated to the third century BCE, and are apparently the most ancient swastikas known to archaeologists. Interesting to note that the Indians received swastikas from neighboring countries only hundreds of years later.
See there also a map of the distribution of the swastika
This map certainly arouses my envy, and I hope that some day we’ll have a similar detailed map of the distribution of the Star of David.