Complex sentence: He also became disillusioned at the discovery that the Inuit had deliberately left the remnants of Franklin's expedition to starve, without considering that it would have been impossible for the local population to support such a large group of supernumeraries.
Split into simpler sentences: He also became disillusioned with the Inuit by the discovery that the remnants of Franklin's expedition had deliberately been left to starve. He failed to consider that it would have been impossible for the local population to support such a large group of supernumeraries.