The last episode of the first season of Spartacus Blood and Sand gave us a bloody and reasonable ending. Spartacus and other gladiators rebelled against Roman nobles, killing more people than any episodes before.
Two main casts, the dominators of gladiators, Batiatus and his wife, finally died by Spartacus and Crixus, who are the future leaders of rebel. But two more evil casts had escaped, looking for revenge. So these two casts might cost the failure of Spartacus rebel.
Another thing will also affect the rebel into failure is that even though Crixus jointed Spartacus, he was still looking for achieving a greater honor than Spartacus. He will break up with Spartacus sooner or later.
