https://en.wikipedia.org/wiki/The_Road_Not_Taken_(short_story)

(http://www.autoadmit.com/thread.php?thread_id=4347473&forum_id=2/en-en/#38863402)

Plot summary

The story is told through limited third person point of view, with most of the story concerning a single Roxolani captain, Togram. During a routine journey of conquest, they happen upon Earth. The Roxolani anticipate a simple and rewarding campaign, as they can detect no use of gravity manipulation, the cornerstone of their civilization. Humanity is awed by the invaders, as the maneuverability granted by that technology suggests the rest of their civilization is equally impressive. But as they begin their assault, things take a turn for the absurd—the Roxolani attack with matchlock weapons and black powder explosives. Humans retaliate with automatic weapons and missiles. The battle is short, and most of the invaders are killed. A few are captured alive.

When they are interrogated, the truth becomes evident: the method of manipulating gravity is absurdly simple, and species like the Roxolani are thus able to use faster than light travel with relatively primitive technological sophistication. This enabled them to engage in wars of conquest on a galactic scale. However, adopting the technology allowing for interstellar travel (and wars of conquest on a galactic scale) stifles further technological development as all the creative energies of societies that find it go into perfecting it. In contrast, humanity somehow missed developing gravity technology and advanced further technologically.

As Togram and another Roxolani captive realize the impact of the narrow but critical Roxolani technology for another, generally more advanced society, the story closes with the two asking themselves, "What have we done?"

(http://www.autoadmit.com/thread.php?thread_id=4347473&forum_id=2/en-en/#38863404)