Cortex Command

The quickest way to do this grind is by entering Control Chip Hunt as the humans side. Once the game starts, press E and quickly move out of bounds to the right, which results in a failure. After this, instead of starting a whole game again just press Ctrl+R to reset this one and it will still count. Do this 999 times; it doesn't take too long to do.

Quick video guide to show how to get this achievement (use the settings I show, it's explained there; just use all 6 different factions to win). If you start a battle just start a new campaign and hope you don't as it'll just be quicker if you avoid the fights themselves entirely.
https://youtu.be/Vq29ex3Os-g