Here's a video on how to obtain ALL of the prologue achievements, and more! Links to the specific achievements, in order of when you'll obtain them, are in the video description. I didn't show battles as some are walked through by the AI, and most others are simply auto fought and won. The last one appears very difficult, but my game cut out, and I didn't complete the prologue.
As for this achievement:
1. Late in the prologue, before the final mission, I was attacked at my home base.
2. I won this battle, and it was my 10th, getting the 10 battle wins achievement. I got this achievement at the same time.
3. For that reason, i'm guessing you can go straight to the final mission, win, and get the achievement.
4. If you're worried, there was lots around the map to fight, and to win 10 battles. You'll get about 9 or so naturally though before finishing the prologue. On that 10th battle win, for me, I became a level 10 Lord.