  We have studied the impact of non-local electronic correlations at all length
scales on the Mott-Hubbard metal-insulator transition in the unfrustrated
two-dimensional Hubbard model. Combining dynamical vertex approximation,
lattice quantum Monte-Carlo and variational cluster approximation, we
demonstrate that scattering at long-range fluctuations, i.e., Slater-like
paramagnons, opens a spectral gap at weak-to-intermediate coupling --
irrespectively of the preformation of localized or short-ranged magnetic
moments. This is the reason, why the two-dimensional Hubbard model is
insulating at low enough temperatures for any (finite) interaction and no
Mott-Hubbard transition is observed.
