Answer
Saxons and Bavarians were the primary tribes that Charlemagne's father Pepin the Short had to contend with during his rule as the Frankish king. To maintain control and consolidate power, Pepin faced numerous rebellions and uprisings from these groups. By successfully suppressing these revolts, he ensured the stability and expansion of the Frankish kingdom, paving the way for his son Charlemagne's later conquests and influence.