What do you mean they didn't have an advanced civilization? They had city densities above the best in Europe and their gold work put European goldsmiths to shame. They had the abacus, pain medications, aqueducts, armor, dams, beer, gold plating along with sintering soldering and lost wax casting, roads, the concept of zero in mathematics, advanced astronomy, plumbing, the suspension bridge, multiple unique writing systems, and tons of food preservation techniques. That is a far cry from some dudes tieing rocks to sticks.