We had learned to fold space, to portal to new worlds faster than thought. We planted flags on many worlds.
This planet seemed like any other. There were creatures, but initial indications pointed to no intelligent life. Only the use of rudimentary tools was captured by our droids.
We were wrong.
The species on this planet were very clever. Most aerial battles resulted in our jets being blown up. Our best dog fighters were no match.
Ground attacks were similarly fated. The locals either hid in the trees and chipped away at our forces or used huge beasts to crush our defences.
It became clear that they had been training their whole lives to defend their planet. Our generals started to wonder, “From who?”