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One usually doesn't speak of an "electrostrong force" because, well, we haven't unified them yet. But someday it might make sense. The Standard Model looks like SU(3) x SU(2) x U(1). The SU(3) part is from quantum chromodynamics, and tells us how quarks work. We can think of them as having three colors, but because of a phenomenon called confinement that still isn't completely understood, the colors are always masked. The SU(2) x U(1) part is the electroweak force and is unified; in particular that U(1) is not the U(1) of electromagnetism, which is a different subgroup of SU(2) x U(1). So in that sense electromagnetism and the weak force are unified. But the combination of that with the strong force is just a direct product of gauge groups, the simplest way of combining them, and so cannot be called unified. They are unified in certain Grand Unified Theories, which embeds the gauge group of the Standard Model within a larger group like SU(5) or E(6). However, so far we have no experimental evidence that any of these theories are true. So, despite widespread expectations that one day we can speak of a unified theory of electromagnetism, the weak force, and the strong force (gravity is a more difficult issue, but we also want a theory of quantum gravity), at the moment the "electrostrong" theory is unknown.