  D-theory provides an alternative lattice regularization of the (1+1)-d
CP(N-1) quantum field theory. In this formulation the continuous classical
CP(N-1) fields emerge from the dimensional reduction of discrete SU(N) quantum
spins. In analogy to Haldane's conjecture, ladders consisting of an even number
of transversely coupled spin chains lead to a CP(N-1) model with vacuum angle
\theta = 0, while an odd number of chains yields \theta = \pi. In contrast to
Wilson's formulation of lattice field theory, in D-theory no sign problem
arises at \theta = \pi, and an efficient cluster algorithm is used to
investigate the \theta-vacuum effects. At \theta = \pi there is a first order
phase transition with spontaneous breaking of charge conjugation symmetry for
CP(N-1) models with N>2.
