  The non-perturbative solution to the strong CP problem with magnetic
monopoles as originally proposed by the author is described. It is shown that
the gauge orbit space with gauge potentials and gauge tranformations restricted
on the space boundary and the globally well-defined gauge subgroup in gauge
theories with a $\theta$ term has a monopole structure if there is a magnetic
monopole in the ordinary space. The Dirac's quantization condition then ensures
that the vacuum angle $\theta$ in the gauge theories must be quantized to have
a well-defined physical wave functional. The quantization rule for $\theta$ is
derived as $\theta=0, 2\pi/n~(n\neq 0)$ with n being the topological charge of
the magnetic monopole. Therefore, the strong CP problem is automatically solved
with the existence of a magnetic monopole of charge $\pm 1$ with $\theta=\pm
2\pi$. This is also true when the total magnetic charge of monopoles are very
large ($|n|\geq 10^92\pi$). The fact that the strong CP violation can be only
so small or vanishing may be a signal for the existence of magnetic monopoles
and the universe is open.
