What is the ideological content expressed in Captain Grant's Children?

Captain Grant was killed when he went to the Pacific Ocean to find an immigrant island for Scottish expatriates in order to oppose England's slavery to Scotland, while Sir Granawan spared no effort to save his compatriots. They are brave, tenacious and fearless, which embodies Verne's progressive thought of opposing slavery and colonialism, and shows the noble quality and lofty humanitarian spirit of maintaining social justice.