  We perform a careful study of the infrared sector of massless non-abelian
gauge theories in four-dimensional Minkowski spacetime using the covariant
phase space formalism, taking into account the boundary contributions arising
from the gauge sector of the theory. Upon quantization, we show that the
boundary contributions lead to an infinite degeneracy of the vacua. The Hilbert
space of the vacuum sector is not only shown to be remarkably simple, but also
universal. We derive a Ward identity that relates the n-point amplitude between
two generic in- and out-vacuum states to the one computed in standard QFT. In
addition, we demonstrate that the familiar single soft gluon theorem and
multiple consecutive soft gluon theorem are consequences of the Ward identity.
