Final answer:
One of the most important aspects to keep in mind when studying history, according to John Green, is the significance of empathy and perspective, or 'historical empathy', which enables understanding the past without contemporary bias.
Step-by-step explanation:
According to John Green, the importance of empathy and perspective is one of the most important things to keep in mind when studying History. This practice, often called historical empathy, involves the ability to understand and meet the past on its own terms, without judging it through modern-day attitudes. By doing so, historians can present the past as clearly as possible and maintain that clarity for future generations, providing a richer and more accurate picture that includes ongoing research into areas like LGBTQ+ studies, Indigenous studies, and the history of the Global South.