Colimits of abelian groups

In this paper we study the colimit N_2(G) of abelian subgroups of a discrete group G. This group is the fundamental group of a subspace B(2,G) of the classifying space BG. We describe N_2(G) for certain groups, and apply our results to study the homotopy type of the space B(2,G). We give a list of classes of groups for which B(2,G) is not an Eilenberg--Maclane space of type K(\pi,1).