There has been a fair bit of discussion about 'Gotochi' postcards on the Postcrossing forum and I don't really have anything to add. I do really like this series, it's a shame the postcards are so expensive and hard to get, though. I've managed to get a few, this one is probably my favourite as I find samurai pretty fascinating.
This postcard is from Niigata Prefecture, a prefecture of Japan located on the island of Honshū on the coast of the Sea of Japan. The capital is the city of Niigata with which it shares the same name. The name "Niigata" literally means "new lagoon".
Until after the Meiji Restoration, the area that is now Niigata Prefecture was divided into Echigo Province and Sado Province. During the Sengoku period, the Nagao clan, who were at times vassals to the Uesugi, ruled a fief in the western part of modern Niigata from Kasugayama Castle. The most notable member of the Nagao clan was Nagao Kagetora, later and better known as Uesugi Kenshin. He unified the leaders of Echigo Province and became its sole ruler. By taking the surname Uesugi, he also became the head of the Uesugi clan and effectively brought their realm under his control.