  In this paper we prove the nonlinear stability of Minkowski space-time with a
translation Killing field. In the presence of such a symmetry, the 3 + 1 vacuum
Einstein equations reduce to the 2 + 1 Einstein equations with a scalar field.
We work in generalised wave coordinates. In this gauge Einstein equations can
be written as a system of quasilinear quadratic wave equations. The main
difficulty in this paper is due to the weaker decay of free solutions to the
wave equation in 2 dimensions, compared to 3 dimensions. This weak decay seems
to be a deterrent for proving a stability result in the usual wave coordinates.
In this paper we construct a suitable generalized wave gauge in which our
system has a "cubic weak null structure", which allows for the proof of global
existence.
