Complex sentence: By the late 70s, Hippe had joined and became one of the leading members of the Latin American Group in Oslo; the organization had around 80 members and had collaborated with Amnesty International on projects involving Latin America.
Split into simpler sentences: By the late 1970s Hippe had joined the Latin American Group in Oslo and became one of its leading members. The organization had around 80 members and had collaborated with Amnesty International on projects involving Latin America.