  We introduce a duality between two-dimensional XY-spin models with
symmetry-breaking perturbations and certain four-dimensional SU(2)and SU(2)/Z_2
gauge theories, compactified on a small spatial circle R^(1,2) x S^1, and
considered at temperatures near the deconfinement transition. In a Euclidean
set up, the theory is defined on R^2 x T^2. Similarly, thermal gauge theories
of higher rank are dual to new families of "affine" XY-spin models with
perturbations. For rank two, these are related to models used to describe the
melting of a 2d crystal with a triangular lattice. The connection is made
through a multi-component electric-magnetic Coulomb gas representation for both
systems. Perturbations in the spin system map to topological defects in the
gauge theory, such as monopole-instantons or magnetic bions, and the vortices
in the spin system map to the electrically charged W-bosons in field theory (or
vice versa, depending on the duality frame). The duality permits one to use the
two-dimensional technology of spin systems to study the thermal deconfinement
and discrete chiral transitions in four-dimensional SU(N) gauge theories with
n_f >=1 adjoint Weyl fermions.
