Is there a single word that is a more vicious connotation of "competition"?

How about "rivalry," "antagonism, and "oppugnancy?"

rivalry: the state or condition of competition or antagonism.

antagonism: an active hostility or opposition, as between unfriendly or conflicting groups.

oppugnancy: the state or quality of being oppugnant; antagonism.

Try death struggle or struggle to the death; such a struggle can last a long time -- for instance in a civil war, which in the worst case can continue for decades.

Consider the following terms:

• rat race, “An activity or situation which is congested with participants and which is hectic or tedious, especially in the context of a busy, modern urban lifestyle”
• slugfest, using a figurative form of the sense “(sports) A game or match in which heavy hits are exchanged”
• infighting, “Fighting or quarreling among the members of a single group or side”, a term that perhaps fits well in the example sentence