I know this is a bit broad, but I would imagine this question better applies to the era when states had begun to form.
Has such a concept of two states declaring their own wars on one nation over the same territory occurred?
How did this affect relations between the independent aggressors?
Just to clarify, you're not asking about a situation like Germany and the USSR vs. Poland in 1939, where the aggressors secretly agreed to partition the invaded country?
You're asking about a situation where the aggressors have mutually exclusive claims and objectives on a third country, right?