We report results obtained for SU(2) Yang-Mills theory on a four dimensional torus with two
directions much smaller than the other two. The small 2-torus is equipped with twisted boundary
conditions. This construction provides a way to interpolate from a region in which semiclassical
methods can be applied (for small 2-torus size) to the standard infinite volume case. Our simu-
lations at small torus sizes show how the topological charge and the string tension result from a
gas of vortex-like fractional instantons. As the size becomes larger the density increases and the
separation of structures tends to a constant in agreement with the fractional instanton liquid model
picture of the Yang-Mills vacuum.