Complex sentence: The organization was successful at blocking the sale of tribal land to non-Indian developers, they successfully fought for control of the MEI board of directors and lobbied Congress to restore their status as a federally recognized sovereign tribe.
Split into simpler sentences: The organization was successful at blocking the sale of tribal land to non-Indian developers. They successfully fought for control of the MEI board of directors and lobbied Congress to restore their status as a federally recognized sovereign tribe.