Almost every year of his reign Charlemagne is forced to go and vanquish the Saxons again and has to re-Christianize them on the spot.
I don`t see any problem in using the present first and then the past, unlike your professor, since the dates (between 1726 and 1815) tell you when the narrated occurrences happen. Besides, he`s free to condemn whatever he pleases in his students`papers, and they have to conform to their teacher`s whims to get a passing grade. In the real world, that`s not how things stand.
Entre 1726 a 1815, los académicos despojan al idioma de muchos colgajos etimológicos y la hacen más sencilla y práctica. Algunos criterios fijados en esa época siguen vigentes hoy, como las reglas de la b y la v y la escritura de c y z. También se cambiaron palabras como dotor, efeto y sinificar por los actuales doctor, efecto y significar.
But I still see a minor mistake in the above paragraph, maybe too a subtle one. Can anybody else spot it?
The verb tense that I found odd, as you guys have pointed out, is the hubiese instead of hubiera. So, here you go, an answer to someone`s question (I can`t remember who now).