Complex sentence: Kangxi knew it would be a mistake to raise his children inside the palace alone; therefore, he exposed his sons (including Yinzhen) to the outside world and gave them a rigorous education.
Split into simpler sentences: Kangxi knew it would be a mistake to raise his children inside the palace alone. Consequently, he exposed his sons (including Yinzhen) to the outside world and gave them a rigorous education.