The American Branch of the Theosophical Society maintain a YouTube channel that includes videos or recent lectures by and to their members as well as documentaries about the Society including archival footage. You can investigate their archives here: https://www.youtube.com/user/TheosophicalSociety.
According to their own website “The Theosophical Society was founded in late 1875, in New York City, by Russian noblewoman Helena Petrovna Blavatsky and American Colonel Henry Steel Olcott, along with attorney William Quan Judge and a number of other individuals interested in the philosophy expounded by Madame Blavatsky.”
Crowley was a fan of Blavatsky’s and the early work of the Society citing that fact that he was born in the same year as the Society’s founding has having deep, positive experience. Crowley’s commentary to Blavatsky’ book “The Voice of the Silence,” saw him ascribing the grade of 8=3 or Magister Templi in the A.’.A.’. to her. He was not quite as fond of the Theosophists he encountered as an adult or its leadership including Annie Besant.
You can read the current administration’s account of the history and current aims of the Theosophical Society here:
At the end of the 19th century the Society schismed. The explanation posted at https://www.theosophical.org/ states:
“During the Ninth Annual Convention of the American Section in 1895, eighty-three lodges voted for autonomy from the international Theosophical Society in Adyar. The international President-Founder, Colonel Olcott, interpreted this action as secession and revoked charters of those lodges, whose members reorganized under the leadership of William Q. Judge. The five American lodges that had opposed the 1895 secession retained their affiliation with the international Society in Adyar. Under the leadership of Alexander Fullerton, they formed a new American Section of the TS known then as the ‘American Theosophical Society.’ Extensive lecture tours by Annie Besant and Constance Wachtmeister elicited much new interest, so that by 1900 our organization claimed 1286 members and 71 branches. The ‘American Theosophical Society’ was legally renamed ‘The Theosophical Society in America’ (TSA) in 1934, and has existed under that name ever since. Like other Theosophical groups, the organization aspires to educate the public about the principles of Theosophy through publications, public programs, and local group activities.”