Hello kiddo! Do you know that in some olden days, when a king or a leader of a country dies, someone from their family would take over as the next king or leader?
Now imagine that the king has no one to become the next leader of the country after they die. That's where the doctrine of lapse comes in.
The doctrine of lapse was a rule created by the British people who were ruling India. It said that when an Indian king died without a son or someone to succeed them, their land would belong to the British government.
So, basically, if the king of a country in India died without having a son or someone to take over, the British would say that their land belongs to the British government. This was mainly done to increase the British territory in India.
Many people in India did not like this rule, as it took away their freedom and made them feel like second-class citizens in their own country. However, this rule was eventually abolished, and India eventually gained independence from British rule.
So, that's the doctrine of lapse, in simple terms!