Complex sentence: In his first appearance, he is allowed into Atlantis despite the protests of many elitist Atlanteans, due to an attempt by Aquaman to make Atlantis more open to citizens living outside the city, by granting them citizenship.
Split into simpler sentences: In his first appearance, he is allowed into Atlantis despite the protests of many elitist Atlanteans. This is due to an attempt by Aquaman to make Atlantis more open to citizens living outside the city, by granting them citizenship.