Complex sentence: Not expecting any real oppositions as they outnumbered the forces of Iga and not expecting their guerrilla tactics he was very humiliatingly defeated by a very underwhelming force and on top of this one of Oda Nobunaga's highly esteemed generals died in this catastrophic campaign.
Split into simpler sentences: Not expecting any real opposition, as they outnumbered the forces of Iga, and not prepared for their guerrilla tactics he was very humiliatingly defeated by a very underwhelming force. On top of this one of Oda Nobunaga's highly esteemed generals died during this catastrophic campaign.