I will describe various ingredients that show up repeatedly in studies of various quantum mechanical gauge theories at large N and how these ingredients related to each other.
The first is that perturbation theory usually leads to a spin chain dynamics. I will show that the same happens in large N QCD on the lattice in the strong coupling expansion. Secondly, states with energies of order N can be D-branes. These can be accounted for by Young diagrams and decorations on them. Third, one can count more general states with Young diagrams and in some examples this point of view provides additional information on possible phase transitions. All along, there seem to be relations between these combinatorial tools and geometric ideas.