Genosha is a nation off the coast of Africa.
The nation promoted themselves as being a safe-haven for mutants. However, it was secretly ruled by Bolivar Trask, Cameron Hodge, Henry Peter Gyrich, and "the Leader" who enslaved all the mutants who arrived. They kidnapped them with Sentinels and forced them to build Master Mold. At one point they captured the X-Men Gambit, Storm, and Jubilee. Gambit got out and joined Cable in freeing the mutants.
Some time later, Magneto took over the country and actually turned it into a mutant safe-haven. However, he argued for domination over humanity. After Professor X was critically injured, Magneto stopped his attack and bid his friend farewell as he went to the Shi'ar Empire with his own love Lilandra to be saved.
First version of the nation outside the comics.