A estrada não tomada, Harry Turtledove :
The story is told through limited third person point of view, with most of the story concerning a single Roxolani captain. 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 Roxolani's method of manipulating gravity is absurdly simple, and they were thus able to begin utilizing aircraft, spacecraft, and even faster than light travel during their Age of Sail.