They had interstellar invasions down to a tee, where as we had yet to even leave the solar system. In hindsight, the invasion tactic was quite simple. Have the superior technology, and conquest is absolute. Don't have the superior technology? Blast the other species with EMPs until you do. And that's what they did.

5 years of medieval era oppression followed before the resistance gained a foothold. The foothold came in the form of a successful covert raid of an enemy's research center. With their technology in our hands the pathetic attempts at resistance became a full fledged war. In an instant, mankind skipped several technological eras, which would have been a blessing to society, if it weren't for the extension level war we now had to fight.

War ravaged the planet for the next 5 years. The scale of the war was so large that no amount of military or political delegation could keep up with the ever dynamic war. The adversary utilized a hive mind to instantaneously orchestrate thousands of elements of the war, and we started loosing. We had to come up with a solution, and fast.

It was the largest project humanity had ever endeavored. So large in fact, that money became irrelevant during its development, and time became the sole constraint in managing the project. And we almost ran out of that too. Just weeks away from loosing the war, PAX was deployed. The first human 'hive mind'. Tasked with orchestrating the war, it delegated every operation down to the individual level. Optimized the actions of every human effort in the war dynamically, and instantaneously. Biological hive mind vs. artificial hive mind....

For the next 3 years the hive minds played a game of 4d chess that amounted to a stalemate in the war. Both hive minds were too optimized, simultaneously launching and parrying thousands of operations at each other, gaining nothing as result. After googles of computations which resulted in battles, assaults, flanks, raids, that were met with equally devised countermeasures, the road to victory became clear, destroy the enemy hive mind without the use of our own.

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Two shades of blue met on a perfectly horizontal horizon in every direction. I looked up, trying to at least find a cloud in the sky to break the monotonous blue, but only found the sails of our boat rippling in the Pacific wind. To avoid being another element calculated into the everlasting chess game between the hive minds, we needed to sail covertly. Meaning no engines, no electricity. Back to the medieval times. We are the uncalculated element, sailing into the enemy's heart, to disrupt this war.