temperatures where the signal is not motionally averaged.[@Jairo; @Yalegrouppapers] It is now clear that disorder plays a role in the interpretation of these experiments, even when it is weak. At stronger disorder, as the non-interacting limit is approached, the spin-polarization must eventually vanish. In our model calculations we find that as the interaction strength is increased relative to disorder at $\nu=1$, the 2DES ground state suffers a continuous phase transition a from paramagnetic to a ferromagnetic state. Depending on the details of the disorder model, a second continuous phase transition to a fully spin-polarized incompressible strong ferromagnet with a gap for charged excitations may occur at still stronger interactions. For the disorder models we use, the fully polarized state is reached when the Coulomb energy scale is approximately twice the Landau-level-broadening disorder energy scale. Away from $\nu=1$, screening by mobile charges reduces the importance of disorder and the system reaches maximal spin-polarization at smaller interaction strengths. The maximally polarized ground state at moderate interaction strengths is best described as a glass of localized conventional quasiparticles formed in the $\nu=1$ fully polarized vacuum. Only for stronger interactions do we find a phase transition to a state with non-collinear magnetization in which 