Comment by yummypaint

A key property of QCD is that unlike electrodynamics, the forces between interacting objects increase with distance (quark confinement). This is what breaks the usual style of expansions used to simplify problems. It's hard to overstate how important this is.

One of the implications is that there are many interactions where most possible Feynman diagrams contribute non-negligibly. The advances in theory arguably have much more to do with improvements in techniques and the applied math used, such as in lattice QCD and Dean Lee's group for instance.