The full record of Earth-23's timeline remains to be revealed.  Many events, including the histories of Earth and Krypton, contain many of the same seminal events as other worlds across multiple timelines.  The prevailing distinction in this timeline is the prevalence of dark skin among it's inhabitants. Two basic concepts could explain this distinction.

First, it is possible that unlike many worlds where exploration and conquest was Euro-centric, Earth-23 may have had Afro-Centric spread of civilization so that the New World and the rise of the United States was lead primarily by immigrants from Africa.  This concept is consistent the prominence of Black Lighting, Steel, Vixen and other heroes who are also Black in other timelines.

Second, it is possible that the level of ambient ultraviolet radiation - the evolutionary driver of melanin in skin - is higher in this universe and thus Black races are the dominant phenotype.  This would explain the similarity between Terrans and Kryptonians.  It it also possible both of these explanations contribute to the unique aspects of the inhabitants of the Earth-23 timeline.

The earliest knowledge of  this timeline occurs from the destruction of the Planet Krypton in the late 20th century.  Realizing the imminent death of their world, scientists Jorel and Lara created a rocket ship that sent their only son Kalel to Earth.  Found by the kindly Ellis family, he was adopted and named Calvin.   By the beginning of the second decade of the 21st century, Calvin had entered politics and achieved the pinnacle of United States governance - The Presidency.

Earth-23 first came to multiversal attention when a legion of Superman was assembled during the Final Crisis to defeat Darkseid and the corrupted monitor Mandarakk (Final Crisis #7).  Further connection to the Multiverse occured when Lois Lane, Jimmy Olsen and Clark Kent arrived from Earth-45 fleeing a monster called Super-Doom that they had inadvertently created as a world saver.   The Superman of Earth-23 eventually defeated Super-Doom though not before the Jimmy Olsen of Earth-45 had died and Clark Kent of that world serious injured (Action Comics Vol2 #9).

Some time later, the advent of the Gentry led to another multiversal crisis.  Heroes from across the multiverse banded together to meet this threat, leading to formation of a multiversal Justice League - Justice League Incarnate (The Multiversity #2).   Superman of Earth-23 became the leader of the League, taking them into battle with Darkseid and Injustice Incarnate (Infinite Frontier #1-6) and  then Pariah and the Dark Army (Justice Incarnate #1-5).  He also joined a band of Superman to defeat the villain Prophecy that was collecting and killing Superman across the Multiverse (Superman Vol. 4 #14-16).

A full understanding of Earth-23, beyond the exploits of its primary champion, remains to be revealed.