Provided is method of making a three-dimensional object comprising polyurea, which may include: (a) dispensing a one part (1K) dual cure resin into a stereolithography apparatus, the resin comprising or consisting essentially of a photoinitiator, a reactive blocked polyisocyanate, optionally a catalyst such as a polyurethane blowing catalyst, and optionally a polyepoxide; (b) additively manufacturing from said resin an intermediate object comprising the light polymerization product of said reactive blocked polyisocyanate; (c) optionally cleaning said intermediate object; and (d) reacting said polymerization product in said intermediate with water in the presence of a catalyst such as a polyurethane blowing catalyst (which may be included in the resin, the water, or both) to generate polyamine in situ that sequentially reacts with the remainder of the polymerization product to form urea linkages and thereby produce a three-dimensional object comprising polyurea. Dual cure resins useful for the method are also provided.