This may just be semantics, but it's always confused me. What is the thesis of Chaos Theory? I have read an entire book about it, and as far as I can tell, its just a bunch of analytical techniques, but there is no underlying object "chaos" that is being characterized, its just a bunch of sophisticated tools for parsing nonlinear dynamical systems.
As a counterexample, Matrix Theory is about the behavior of vector spaces and operations on them, the theory of linear ODEs leads to elegant proofs of some properties. But what are some proofs/theorems about "chaos" -- the closest thing I can find is that phase-space trajectories have a positive Lyapunov exponent...there must be more than that!
Nonlinear dynamical systems can be quite roughly divided in two huge realms: the realm of order (continuous time two dimensional systems) and the realm of chaos (dimension three and above for continuous time systems).
The former is mostly about 16'th Hilbert problem about the number of limit cycles on the plane and still is a huge area of research. The other one is about most "hyperbolicity" and how to classify the flows in higher dimensions. So, despite the cynical comment of @ AndreNicolas, there is an excellent reason to talk about Chaos theory.