  We give a new proof of the equivalence between two of the main models for
$(\infty,n)$-categories, namely the $n$-fold Segal spaces of Barwick and the
$\Theta_{n}$-spaces of Rezk, by proving that these are algebras for the same
monad on the $\infty$-category of $n$-globular spaces. The proof works for a
broad class of $\infty$-categories that includes all $\infty$-topoi.
