Theosophy, loosely meaning "divine wisdom" or "wise god," got its start in the late 19th Century. And for that, we mainly have Helena Petrovna Blavatsky to thank. Madame Blavatsky, as she was often called, was a con artist with a Messiah complex. Although she claimed to have studied under Indian gurus and Tibetan sages, apparently most of what she learned from them was a nice group of parlor tricks -- one famous story has her "materializing" a teacup out of thin air.
The Theosophical Society, founded in New York in 1875 by Blavatsky and two others, proposed that all the religions of the world are, deep down, pretty much the same thing. To put it in modern parlance, there's really no need for us to keep blowing each other up. Pity that that underlying point proceeded to get muddled up in all of the dogma of theosophy, a belief system that at first proposed to be dogmaless but then went on to claim that Atlanteans invented airplanes and explosives thousands of years ago. Whatever.
Since then, the Theosophical Society has spread all over the world. It lets guest speakers share their views while the society puts forth the mantra that we are all interconnected. Everything is One. Very Zen. Supposedly, we'll solve all the world's problems once we realize that. Don't hold your breath.