If you can keep all (or most) of the AI factions going until about 150BC, then you'll face elite armies all over the place. Until the AI has a massive number of large, well upgraded cities, it'll happily churn out the rubbish militia and bog-standard troops for fun.

One way to slow down your progress is to only train units once per year (either the summer or winter turn). Then in theory, the AI can train its armies twice as fast, which is handy as it always needs replacements for the thousands of men it throws away at you.