In a lot of shows, the stakes in the plot are raised kind of arbitrarily; a bigger, more dangerous baddie shows up out of nowhere.
In SG-1, the stakes get raised *because* humanity is learning and working their way through the problem. The team learns how to solve problems, only to open the door to harder, more dangerous problems. The stakes get raised as humanity gains power and the Goa'uld are forced to take them more seriously.
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