If you can have millitairy superiority, there is no reason to worry about being behind in techs.
If you use artillery, you don't need to have the most modern units. Artillery even with cavalry can stand against much more modern warfare with no problems as long as you have enough of them. If your advisor tells you your millitairy power is average or strong compared to your opponents, things are ok.
This way, you can simply conquer your opponents without the need for the latest technology. You can also get some new technologies when your victim wants to talk about piece after you took some of his cities.
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